Hybrid metal/metal composites are attracting great attention globally for low-carbon manufacturing because they can be ultra-light and have a good combination of mechanical and other desired properties. The application of hybrid metal/metal curved composite profiles to replace traditional curved sections can give full play to the advantages of composite materials. To examine the feasibility of forming such profiles, an aluminium/magnesium metal hybrid curved section was manufactured using a newly developed differential velocity sideways extrusion (DVSE) process. A bimetallic billet comprising a magnesium cylinder enclosed by an aluminium tube was extruded using different speed settings on the two extrusion punches to give precisely controlled radii of curvature in the product. The mechanics of deformation were studied using practical experiments and process modelling, and the microstructural and mechanical properties of the extruded section were determined. It has been demonstrated that the DVSE process with appropriately chosen punch speed settings transforms an initially straight billet with its magnesium core and aluminium cladding into a curved extrudate comprising two discrete magnesium cores surrounded well by aluminium, with a harder surface layer. A monotonic relationship is found between the curvature and the ratio between the speeds of the two punches. The DVSE process induces grain refinement in both the aluminium and magnesium layers with respect to the initial billet. In the aluminium layers, continuous dynamic recrystallisation is the dominant grain refinement mechanism, whereas in the magnesium layers, the fine grains are {1012} tension twins. The present study shows the potential of the novel DVSE process for the production of variable-curvature hybrid metal/metal composites with a good combination of desired properties.

Lightweight curved profiles are widely utilised in the transportation industry considering the increasing need for improving aerodynamic efficiency, aesthetics and cutting emissions. In this paper, curved AZ31 Mg alloy profiles were manufactured in one operation by a novel process, differential velocity sideways extrusion (DVSE), in which two opposed rams were used. Effects of extrusion temperature and velocity (strain rate) on curvature, microstructure, and mechanical properties of the formed profiles were examined. Profile curvature was found to be more readily controlled by the velocity ratio of the bottom ram v2 to the top ram v1, whereas extrusion temperature (T = 250, 300, 350 °C) and extrusion velocity (v1 = 0.1, 1 mm/s) slightly affect curvature for a given velocity ratio. A homogeneous microstructure with equiaxed grains (∼ 4.5 µm) resulted from dynamic recrystallisation (DRX), was observed after DVSE (v2/v1 = 1/2) at 300 °C and v1 = 0.1 mm/s, where the initial billet had an average grain size of ∼25 um. Increasing extrusion temperature leads to grain growth (∼ 5 µm) at 350 °C and v1 = 0.1 mm/s. DRX is incomplete at the relatively low temperature of 250 °C (v1 = 0.1 mm/s), and higher strain rate with v1 = 1 mm/s (T = 300 °C), resulting in inhomogeneous bi-modal necklace pattern grains ranging in size around 1-25 µm for the former and 2-20 µm for the latter. Grain refinement is attributed to DRX during the severe plastic deformation (SPD) arising in DVSE, and initiates at the prior boundaries of coarse grains in a necklace-like manner. Compared with the billet, micro-hardness and ultimate tensile strength of the profiles have been enhanced, which is compatible with grain refinement. Also, an obvious increase in tensile ductility was found. However, yield strength slightly decreases except for the complete DRXed case (300 °C, v1 = 0.1 mm/s), where a slightly higher value was found, indicating strengthening by grain refinement is greater than softening caused by texture modification. The initial billet had a strong basal texture wherein the {0002} basal plane is oriented parallel to the extrusion direction ('hard' orientation), while DVSE results in the profiles having weak basal textures and the {0002} basal plane oriented ∼ 5-10o to the extrusion direction (i.e. towards the orientation for easier slip). This significantly modified texture contributes to the softening of the profiles in the extrusion direction, in which tensile tests were performed, and the related elongation improvement.

The process of Hot Form and Quench of aluminum alloys, called Direct HFQ®, has been developed and applied to manufacture high-strength panel components, in which aluminum alloy sheet is heated to solution heat treatment temperature, quickly transferred to cold press dies, simultaneously formed and quenched, and subsequently artificially aged. For Direct HFQ, however, forming occurs at high temperatures, which results in high workpiece/die friction and wear, and hence high tooling and maintenance costs. In the present study, a novel Indirect HFQ for aluminum alloys has been proposed, in which alloy sheet in the O temper is formed at room temperature, then heated to solution heat treatment temperature, and quickly transferred to cold press dies for shape calibration and quenching, followed by artificial aging. In order to compare Indirect HFQ with Direct HFQ, AA6082 sheet specimens have been deformed uniaxially using the two HFQ techniques to a given strain or fracture. Mechanical properties of the deformed specimens have been measured, and differences in mechanical properties after the two HFQ processes have been quantified. Their microstructures have also been characterized to explain those differences. In addition, both HFQ techniques have been applied to form a B-pillar sectional component. It has been found that grain growth occurs in alloy deformed uniaxially to a strain higher than or equal to 10% during Indirect HFQ process, and the degree of grain growth decreases with increasing deformation. The grain growth during Indirect HFQ leads to a lower yield strength (up to ∼8%) and tensile strength (up to ∼12%) than that of the alloy processed using Direct HFQ. In addition, the alloy has a lower ductility and formability during Indirect HFQ than Direct HFQ.

An analytical model providing a detailed description of the material flow and deformation behaviour of extruded curved profiles produced by the novel differential velocity sideways extrusion (DVSE) process, has been developed on the basis of a unified stream function and the upper bound theorem. Plasticine experiments and finite element (FE) modelling were carried out to validate the proposed analytical model. The derived streamline equation contains a shape parameter n describing the degree of curvature of a flow line and the coordinate parameters x0 and y0 defining entering and leaving positions respectively of the flow line, from the plastic deformation zone (PDZ). The analytical model was able to closely model the material flow eccentricity ratio xi (the relative amounts of work-piece material entering the deformation zone from two opposing directions), and flow lines obtained from experiments under different velocity ratios and extrusion ratios. The predicted value of xi was found to be independent of n value and hardening of the material. The n value was found to increase from the corner near the die orifice to the corner around the dead material zone (DMZ). In addition, the n value increased with the increase of extrusion ratio and ratio of velocities of the two opposing extrusion rams, which enabled the representation of a decreased area of DMZ and more localised PDZ containing 1-99% accumulated effective strain. The predicted field distributions of the localised effective strain rate in the PDZ and inhomogeneous effective strain in the extrudates were consistent with FE modelling results.

In analysing metal forming processes the deformation mechanism map (elastic-plastic, elastic-viscoplastic, or creep type behaviour) for a particular process is commonly built solely in relation to temperature; which can be acceptable for a defined modest strain rate range. However, for a given temperature, if strain rate variation is large, the deformation mechanism could vary significantly. In this paper, a deformation mechanism map is proposed to clarify the interacting effect of deformation conditions (temperature and strain rate) on workpiece behaviour in metal forming processes. Rate type deformation equations which can be used to comprehensively model the effect of temperature and strain rate on deformation mechanism characteristics are elucidated and as examples, determined for Ti–6Al–4V and Al–Mg alloy.

Recently, a biaxial test method comprising a cruciform specimen design and spatio-temporal method to determine the limit strains has been proposed for the determination of forming limit curves (FLCs) and fracture forming limit curves (FFLCs) for sheet metals. However, this test method has not yet been validated against the existing standard methods. In the present work, this biaxial test method has been applied to the aluminium alloy AA5754 for formability evaluation at room temperature and results from the biaxial test method have been compared with those from the standard Nakajima method. Theoretical analysis has been carried out to compare equi-biaxial tension cases for the two methods; a similar variation of thickness strain with radial distance normalised by the radius of the gauge area is found between the two methods. In the biaxial tests, decreasing the radius of the through-thickness dome profile, with which the gauge area is thinned, leads to fracture nearer the specimen centre but produces a less uniform strain distribution. Importantly, the major strains at necking on the FLC, as determined using the biaxial and the standard test methods, are almost the same in the plane-strain state, while in other strain states, the major strains are slightly lower for the biaxial method than that for the Nakajima method. An FFLC for AA5754 has also been determined using the biaxial test method, in which the major strain at fracture decreases with increasing strain ratio β from −0.5 to 0, while it changes only slightly when β > 0.

The metal forming industry is responding to changing technical and commercial demands of customers and increasingly stringent legislative restrictions. In addition, on demand delivery requires lead times having to contract. Also Original Equipment Manufacturers are demanding deliveries just-in-time on changeable schedules and for many products batch quantities have become smaller than they were a few years ago. Thus, lead times must be shortened. To meet these challenges, in the metal forming industry, the rate at which new and existing process technologies and production practices are being developed is increasing. Computer-aided design and manufacturing systems have been allied to computer process simulation, to form powerful Cloud based, knowledge-based tools for producing parts right-first-time through identifying the customers’ needs. The purpose of this paper is to illustrate the contribution made by the authors to enhance the added value of metal formed parts, through advancing scientific process knowledge and developing software to support computer-aided manufacture.

During hot forming of high-strength 7xxx series alloy, friction and galling often occur on the contact surface, degrade product surfaces quality, and affect severely by the process parameters, especially by load and speed. In the present paper, the effect of process parameters, namely applied load and sliding speed, on high-temperature friction and galling performance of AA7075 sheets has been determined using linear sliding tests at 350 degrees C in simulated hot forming. The microscopic observations, i.e., scanning electron microscopy (SEM) and three-dimensional confocal scanning optical microscopy, were utilized to analyze hard phase distribution of the alloy as well as surface and sub-surface of the posttest specimens. A friction model was proposed to describe the friction mechanism. The results show that wear rate gradually decreased with increasing load and speed, attributing to the formed compacted oxide layer on the worn surface, which inhibited the rate of further attrition. Besides, for all test conditions, adhesion dominated the wear mechanism, and the compacted layer was damaged more serious due to more initiation of micro-cracks between hard phase and matrix and higher contact interface temperature at higher load and speed, thus the extent of adhesion is grievous resulting in a higher wear loss.

Extruded profiles/sections are increasingly used in the transport industry for lightweight structures. In this paper, a wide thin-ribbed aluminium profile with asymmetric Z-shape, was manufactured by a novel sideways extrusion process proposed by the authors. A comparative study was conducted by utilising the direct/forward extrusion process at the same extrusion temperature and speed, in which the different process mechanics, resulting microstructures and mechanical properties of profiles have been investigated by experiments and finite element modelling. It was revealed that, compared with sideways extrusion, although the design of a die pocket in forward extrusion induces preform and avoids the use of the large-diameter billet and extrusion container/press needed for extruding wide profiles, it requires a greater extrusion force due to work-piece upsetting necessary to fill the die pocket and leads to a lower effective strain in the profile rib. EBSD characterisation of the regions with an equal effective strain indicated that an increased shear strain is more efficient for obtaining fine grains with a higher average misorientation angle. In the same region of the profile rib made from the two different processes, sideways extrusion results in greater grain refinement due to greater effective strains, and a slightly greater texture intensity was found due to the intensive shear deformation. Tensile tests on formed profiles revealed that sideways extrusion leads to a higher yield strength (YS) and ultimate tensile strength (UTS) but a relatively lower elongation to failure, due to the combined effects of grain refinement, GND and texture intensity enhancement. Compared with the billet, the profile formed by forward and sideways extrusion has a YS increased by about 60% and 79% respectively, and an UTS increased by about 74% and 80% respectively in the extrusion direction, demonstrating an advantage of the sideways extrusion process in improving material strength under the same extrusion condition.

Reduction in vehicle weight can significantly reduce energy use in human transportation. However, to gauge efficiency, energy use and weight for a particular vehicle should be related to the number of people being transported while currently there is no convenient means to assess this. Here we statistically analyse the weight, energy consumption, carrying capacity and occupancy level for automobiles, buses, high-speed trains and aircraft. Based on the analysis and inspired by the medical body mass index (BMI), we have proposed a vehicle mass index (VMI), defined as I=A(WtvWtp)n, for the first time enables energy efficiency assessment of different transportations on a global scale, where n a weight sensitivity parameter and A the energy efficiency constant of a theoretically weightless vehicle. We show the VMI ranges and conclude the significant vehicle weight reduction windows to achieve their index lower limits. The possible limits for the VMI and the associated A and n values are also assessed. The concept of VMI could form the basis of a worldwide standard, useful in the current drive for a greener economy.

In this paper a new extrusion technology, in which two punches are used, and its application to forming lightweight curved structural profiles, is described. The technology is known as differential velocity sideway extrusion (DVSE) and can include, hot extrusion (DVSE-HE), welding extrusion (DVSE-WE), and co-extrusion (DVSE-CE), which have been widely used for curved thin-walled profiles, tubes, and aluminum/magnesium sandwich hybrid bars. By tailoring extrusion temperature, speed, and speed ratio of the punches, a thin-walled profile (~ 1 mm thickness) with small bending radius (less than its width), has been fabricated using DVSE-HE. Using DVSE-WE, two billets were welded in an extrusion die and extruded into a curved tube, in which the welding interface was eliminated. Utilization of DVSE-CE by inserting a magnesium bar into an aluminum tube to form a billet, co-extrusion enabled an aluminum/magnesium sandwich bar with Al as sleeves, to be obtained. These newly developed DVSE techniques illustrate the potential for forming curved lightweight structural parts using a single operation.

Hot stamping technologies require new methods for evaluating formability of sheet metal under various forming conditions. Biaxial tensile testing method using a cruciform specimen has been used for the applications, but a suitable cruciform specimen design has not yet been accepted. One of the challenges in designing a specimen for formability tests is to ensure proportional equi-biaxial strain paths arise at the location of fracture initiation. In this study, after reviewing existing cruciform specimen designs, three different geometries of cruciform specimen, named Type I, Type II and Type III, were proposed. Using numerical analysis and practical experiments, fracture initiation locations and corresponding strain paths in the specimens were investigated under equi-biaxial tension. Numerical simulations were performed to optimise the dimensions of Type I specimen to achieve a relatively high strain level near the centre point of the specimen. Based on the optimised dimensions, equi-biaxial tensile tests were carried out on cruciform specimens with different geometries, and strain paths at the fracture initiation locations were compared and analysed. It was found that in all cruciform specimens, equi-biaxial strain state appears only near the centre point. In the Type I and Type II specimens, fracture never initiates near the centre point, but at a location in the fillet transition zone where major strain is higher than that at the centre point. The Type III specimens have the ability to initiate fracture near the centre point, and to produce proportional strain paths with strain ratio close to 1 in equi-biaxial tension, 0 in plane-strain tension, and -0.5 in uniaxial tension at the locations of fracture initiation. The research provides a cruciform specimen design, Type III, which has high potential to be used for evaluating formability for sheet metal.

Forming limit diagrams (FLDs) and fracture forming limit diagrams (FFLDs) have been widely used to evaluate formability of sheet metals. There are many existing methods for determining localised necking strain and fracture strain necessary to construct these diagrams, however, none has been widely accepted and applied to the range of available formability testing methods, e.g. Nakajima tests and biaxial tensile tests. In this study, a novel spatio-temporal method is proposed and developed for determining the localised necking strain and the fracture strain in deformed sheet metals. In the method, localised necking is assumed to appear at the beginning of an increasing difference between average thickness strain within two rectangular zones where localised necking occurs. The effects of dimensions of the two zones on determined localised necking strains were investigated using uniaxial tensile tests for three sheet metals: AA7075, boron steel and AA6082, and the optimal dimensions are recommended to ensure accurate determinations. In comparison with several widely used existing methods, it was concluded that the novel method has greater simplicity, stability and accuracy in determining the localised necking strains. The method was also successfully applied to determine the localised necking strain and the fracture strain for AA5754 in biaxial tensile tests and it was demonstrated to be unaffected by noise and the Portevin–Le Châtelier (PLC) effect.

In the present investigation, effects of length and geometry of die land/bearing on curved profiles/sections produced by a novel process, differential velocity sideways extrusion (DVSE), were studied through physical experiments using plasticine as a model material and finite element modelling. Profile curvature decreases as die land length increases due to its negative influence on exit velocity gradient, and a straight profile is extruded when the ratio of die land length to die orifice diameter exceeds a critical value l0 which increases as extrusion ratio λ increases and extrusion velocity ratio v2/v1 decreases. Generally, effective strain level of the extrudate slightly increases as the die land length increases. Larger die land length increases the frictional areas between extrudate surface layers and die land (and mandrel for tube extrusion), generating zone of shear along the profile edge and thus increases surface layer effective strain. As a result, the strain homogeneity over the cross-section or wall thickness (for tube extrusion) is decreased. Compared with a sharp die land/container transition corner, a chamfered or radiused die land transition corner leads to an increased curvature due to the decreased effective land length, while it decreases overall effective strain level in the cross-section and strain homogeneity as a result of lower effective strain rate across the deforming region. A sharp die land transition corner is recommended for achieving a relatively large and homogenous effective strain in the cross-section.

The cooling system is a critical element in tooling for hot stamping high-strength aluminium alloys, for which very high quenching rates are required to ensure a supersaturated solid solution state in formed parts. To enhance cooling, ducts within the tools should be close and conformal to the surface die profile. Currently, ducts with curved profiles are made by drilling short straight lengths in die segments which are clamped together to form a complete die, which is expensive and hard to achieve the shape of duct with best cooling performance. To address these disadvantages, a novel method which enables efficient manufacture of conformal cooling systems by embedding a network of tubular cooling ducts within a cast matrix is presented in this paper. The feasibility of the proposed method of making ducts in the hot stamping die is demonstrated. Both experimental and computer-based die quenching tests using heated aluminium test pieces were undertaken to determine the cooling performance of a laboratory-scale tool set with cooling ducts. Simulations using the validated FE model were performed to investigate the effects of cross-sectional geometry, material and duct layout, on the quenching performance of the tools. It was found that ducts made of mild steel perform sufficiently well to make the use of high conductivity copper unnecessary. For a flat die surface, square section ducts provided highest cooling rates in comparison with circular and diagonal ones. The uniformity of die temperature increases with the decreased distance between neighbouring ducts, which indicates that a minimal gap is recommended without deteriorating tool strength. The developed tooling technology has the potential to provide a low-cost, highly efficient method of making conformal cooling ducts because the hot stamping die of high-strength aluminium alloy panels requires larger dimension, greater complexity and higher quenching rates.

Hot form Quench (HFQ (R)) represents a leading-edge hot sheet stamping technology for manufacturing complex-shaped high strength aluminium alloy panel components. Transfer of sheet blank from the furnace to the press is the first crucial step in the process. This paper reports work in which the effects of the blank transfer on the deformation of material during pressing and on the final properties after ageing through thermal-mechanical testing and microstructural observations. Two aluminium alloys are investigated, 6082 and 7075. Hardness, quasi-static uniaxial tensile measurements and TEM microstructure observations provide evidence that post-treatment properties and the underlying microstructure are strongly influenced by the blank transfer step. Severe deterioration in the post-treatment strength was observed for blank transfer temperature, ranging from 250 degrees C to 400 degrees C. The temperature-time-property (TTP) diagrams showed that 350 degrees C was the most sensitive temperature that reduced the post-treatment strength by 45% within 10 s holding. As evidenced by TEM, typical coarse eta and S precipitates at high temperatures were identified, which resulted in different post-treatment properties and hot deformation behavior. Finally, the results from HFQ (R) technology processed aluminium alloys 7075 and 6082 were compared with conventional TTP diagrams, enabling comparison with conventional scientific understanding of quenching effects.

For structural and aerodynamic reasons, curved profiles are widely used in the transport industry for manufacturing lightweight structures. In the present work, a curved AA1050 bar with fine grains and high strength was manufactured by a novel forming technique, differential velocity sideways extrusion (DVSE). The evolution of grain structure and micro-texture during DVSE and the mechanical properties of the formed bar were studied, and the grain refinement mechanism was revealed. Due to the severe strains arising in the process, (greater than that for conventional one pass equal channel angular extrusion), significant grain refinement in the curved bar (grain size similar to 3 mu m) was achieved from the original billet (grain size similar to 357 mu m) in one extrusion operation. Coarse band-like structures containing subgrains with low angle boundaries in the shearing zone gradually transformed into fine shear band-like structures containing equiaxed (sub)grains with a mixture of low and high angle boundaries. The fine shear band-like structures inclined approximately along the shear intersection planes. Severe plastic deformation induced a high dislocation density that initiated subgrain walls with low angle boundaries, which gradually transformed into grain boundaries with high misorientation, indicating that refinement of AA1050 grains in the DVSE process is due mainly to continuous dynamic recrystallization (cDRX). Due to the appearance of greater effective strain on the inner bend of the extruded bar, the grain refinement degree and high angle boundary fraction of the material on the inner bend are slightly greater than those of the material on the outside. DVSE resulted in a weak C-type shear-texture component which can be determined by a proper rotation of the negative simple shear texture. Compared with the billet, significant increase of the hardness, yield strength and ultimate tensile strength by 134.8%, 354.0% and 116.8% respectively was achieved in the formed curved bar, although the elongation to fracture was decreased by 60.0%.

Developing a fast-ageing treatment can significantly reduce the current processing time (180 degrees C x 9 h) of high strength AA6082 automotive components. In this study, a fast ageing treatment in supersaturated solid solution state was developed, such that the mechanical properties can be rapidly achieved after the paint bake (PB) treatment through introducing a pre-ageing (PA) treatment. The determined fast ageing method considered effects of temperature & time, heating rate and subsequent PB on the ageing response. Tensile tests and TEM observations of typical conditions were undertaken to examine evolved strength and precipitate distribution. Results showed that 210 degrees C was the optimum pre-ageing temperature as uniformly sized and distributed small precipitates were obtained. The final strength of about 280 MPa, that is 95% of the nominal strength for T6 temper, can be obtained within 15 min soaking for fast heating, and nearly this value for slow heating. More prolific nucleation occurred during slow heating, resulting in more finely distributed precipitates and a higher strengthening. It was observed that PB further increased the strength of over-aged alloy pre-aged at a high temperature of 240 degrees C. The subsequent PB enabled further nucleation of small clusters and growth of the pre-ageing-induced precipitates which were smaller than 20 nm. This resulted in an improvement in the material strength potentially to satisfy the safety requirements in automotive industry. (C) 2019 Elsevier B.V. All rights reserved.

Forming at elevated temperatures can significantly increase the ductility of aluminium alloys enabling the manufacture of complex-shaped panel components from sheets. This study describes and investigates two elevated temperature forming processes: Hot Form Quench (HFQ (R)) (Lin et al., 2008) and conventional hot forming (HF) of aluminium alloys, with various material condition and processing parameters in order to advance the understanding of forming characteristics and post-formed strength. High temperature uniaxial tensile tests of AA7075 under HFQ (R) and HF conditions were performed to compare the stress-strain behaviors, ductility, and post-formed hardness. The results have shown that the ductility for HFQ (R) condition was greater than that for the HF condition when forming temperature was below 400 degrees C. In addition, typical microstructural evolution, such as the low-melting phase of HFQ (R) and precipitation of HF, were identified using fracture morphology observations and used to explain ductility differences exhibited in these processes. Post-formed hardness resulting from HF with different initial alloy temper and forming conditions were determined and compared with those from HFQ (R). Severe reduction in hardness was found for HF using both high quench-sensitive alloy AA7075 and low quench-sensitive alloy AA6082. For the first time, the effects of a variety of influencing factors are investigated systematically, including heating rate, initial alloy, temperature and strain rate, on the high temperature deformation and post-formed strength of heat-treatable aluminium alloys, which contributes to the thorough understanding of the correlation between forming conditions and microstructural evolutions.

The performed research has, for the first time, investigated and compared the drawability of AA6082 at a comparable temperature range between two elevated temperature forming processes: termed (i) Low Temperature Hot Form and Quench (LT-HFQ (R)) or pre-cooled HFQ (R), patented by Adam et al. (2015) and (ii) Direct Heating Aluminium Forming (DHAF) which represents a refinement of conventional warm forming targeting a higher temperature range. A series of uniaxial tensile and cylindrical deep drawing experiments were conducted. According to uniaxial tensile test results, the most obvious work-hardening and reasonable ductility was observed under LT-HFQ (R) at a deformation temperature of 350 degrees C and strain rate of 1s(-1), which can enhance drawability. For deep drawing experiments, it was found that preheating conditions of each process prior to forming significantly affected forming characteristics and post-formed hardness of the alloy; both the achieved maximum Draw ratio (DR) and limit Blank Holding Force (BHF) at some specific process parameters were increased under LT-HFQ (R). Forming speed and temperature had significant effects on alloy deformation and thus drawability for both processes. In addition, by evaluating the post-formed hardness, process drawability and microstructural evolutions under different processes were simultaneously analyzed.