Friction-stir-welding process has become an established solid-state technique for joining of dissimilar lightweight materials over the past decade by overcoming fundamental welding challenges such as solidification cracking, phase segregation and surface oxidation. Despite these unique capabilities, the resulting microstructure feature in the weld zone consisting of fine grains with a high dislocation density, challenges further heat treatment and forming processes. Hence, a high solution annealing temperature results in degradation of the adjusted microstructure and in a lower to reduced mechanical properties in case of dissimilar joints of precipitation-hardenable aluminum alloys. Subsequent hot forming therefore involves a great effort and requires further heat treatment steps. Thus, the present study investigates the effect of a recently introduced novel thermo-mechanical forming process on local deformation behavior of similar as well as dissimilar joints processed by friction-stir-welding technique of thin-walled AA6082 and AA7075 blanks. To avoid the complete elimination of the adjusted microstructure, the welding process is performed after a thermo-mechanical process consisting of solution annealing, die cooling and peak aging. Uniaxial tensile tests are then carried out at high strain rates ranging from (sic) = 40 s(-1) to (sic) = 400 s(-1). The results show an increase in yield and ultimate tensile strength as well as in total elongation after failure with increasing strain rates. As the strain rate increases, the flow stress of similar weld of AA7075 is higher than those of AA6082 and the dissimilar weld of AA6082 and AA7075. Local deformation measurements reveal higher strain localization in the welded zone for similar welds, which leads to micro-crack initiation and failure due to strain accumulation. Microstructure analysis shows very fine equiaxed grain structure in the nugget zone and homogenous distribution of precipitates after friction stir welding process, which explain the plastic deformation behavior.

The present work investigates the effect of the coupled thermo-mechanical phenomena that occur when applying differential cooling technology by heated and cooled forming tool segments established in functional gradation by press hardening of high strength steel to precipitation-hardenable aluminum alloy AA7075. This application aims at creating graded mechanical properties within one part by a distribution of tailored microstructures. The distribution of the detected precipitations after aging presumably influenced by the spatial variation of the contact cooling rate prior to aging is correlated to the measured sigmoidal hardness profile. Different types and morphologies of precipitates are observed at characteristic positions of the part. The formation of fine and uniformly distributed precipitates at the zones with hardness values of 180 HV is associated to the high cooling rate by low tool segment temperatures. At the same time, coarse and lath-shaped particles are detected at regions with a low hardness value of 123 HV attributed to the lower cooling rate at heated tool segments.

In the present work low-cycle fatigue experiments were carried out on thermo-mechanically processed AA6082 and AA7075 sheets to evaluate mechanical properties under cyclic loading. Different cooling rates imposed by use of tempered forming tools after solutionizing and subsequent aging treatment led to the formation of precipitates with differing sizes and morphologies. Specimens thermo-mechanically processed in tools with temperatures of 24 C and 200 C showed superior mechanical properties under both monotonic and cyclic loading. Different behavior was observed for the specimens formed in the tool with a temperature of 350 C. Based on thorough analysis of prevalent microstructural features, processing-property-damage relationships are established pointing at the major impact of the thermal history on the final performance of the high-strength aluminum alloys in focus.

The usage of wood as an environmentally friendly material combines optimized room aesthetics with mechanical and/or acoustic functionality.Cellular materials like wood play an important role in reducing vibration and noise.It is considered to have low damping properties due to its molecular structure and its relatively high modulus of elasticity.This property is well known to musical instrument makers and is accordingly taken into consideration in the manufacture of such instruments.Site-specific, targeted wooden cladding can help to dampen vibrations.Against the background of noise and vibration control, wooden plates in the form of connected bodies are often used, e.g. to build an enclosure.The vibration behaviour of the resonance body of a wooden musical instrument is difficult to determine.In this context, basic acoustic investigations into the radiation efficiency of wooden panels become mandatory.The solutions to the equation of motion of the vibrating plate depend, among others, on the geometry of the plate and the conditions of its clamping.A fact that makes it very challenging to predict is e.g.eccentric load application that causes much more natural vibrations.In this paper, a plate made of the tonewood spruce was mechanically excited in the centre on the back.The acoustic intensity of the panel on the other side was then measured as a spatial function using an acoustic sensor.Since the clamping conditions influence the vibration characteristics, the measurements were conducted under different clamping loads.A relatively stable mode pattern emerged that was more pronounced at the highest clamping load.

In this study forming tools temperated at 24 degrees C and 350 degrees C were used to systematically investigate the influence of different cooling rates on the mechanical and corrosion properties of a high strength aluminum alloy AA7075 within a novel thermo-mechanical process that combines forming and quenching simultaneously. The samples formed within heated tools reveal higher ductility and lower material strength compared to the parts processed in cold tools. In addition, the corrosion behavior changed between samples formed with 24 degrees C forming tools and 350 degrees C forming tools, respectively. Through cyclic polarization in chloride containing aqueous media a change in the hysteresis and shift of open circuit potential was observed. Metallographic investigation revealed that there was also a very different corrosion morphology for the samples formed within the heated tools. No change in average grain size could be detected but changes of the microstructure in subgrain scale that occur during the forming within the heated tools are responsible for this effect. In further research, the effect of various cooling rates on mechanical and corrosion behavior and the microstructure will be investigated by variation of the forming tool temperature.

The effect of a novel thermo-mechanical process route on quench-induced precipitates morphology and mechanical properties of high strength AA7075 aluminum alloy is investigated in the present work. After solutionizing the probed material is hot formed and quenched at different tool temperatures ranging from 24 to 350 ?C to determine the influence of different cooling rates. The strengthening mechanisms and precipitation morphology after aging are examined based on mechanical testing, microstructure observation and differential scanning calorimetry. The results demonstrate that the tool temperature, as a key element of the investigated process, affects significantly the material strength due to a fundamental change in the microstructure and the strain hardening behavior when exceeding a temperature limit. At tool temperatures from 24 to 200 ?C only a slight decrease in tensile strength from 590 to 568 MPa is obtained. When increasing the tool temperature above 200 ?C, up to 350 ?C, the tensile strength drops to 336 MPa and the initial strain hardening rate ?0 increases. This behavior is linked to the change of quench-induced precipitates morphology and shape. TEM investigations revealed high fractions of semi coherent ??-phases for low and coarse ?-phases for high tool temperatures causing a fundamental shift of strengthening mechanisms from predominantly particle shearing to a combination of bypassing and strain hardening by Orowan loops. High diffusion rates and local accumulation of solute atoms at grain boundaries during cooling led to the formation of large grain boundary precipitates during aging, even after high cooling rate using cooled tools.

Abstract The present work focuses on the effect of thermo-mechanical processing on the mechanical properties and microstructural evolution of AA6082 and AA7075 aluminum alloys using a novel forming process, i. e. integrating solution heat treatment, hot forming and tool quenching. Different tool temperatures ranging from 24 °C to 350 °C were applied to investigate their influence on mechanical strength and ductility. By using various tool temperatures, this study aims to provide insights needed for tailoring the mechanical properties of two different high-strength aluminum alloys. Further it is shown, how the different resulting cooling rates affect the final property distribution. Upon processing, uniaxial tensile tests were carried out at room temperature to characterize the mechanical properties of the investigated conditions. Microstructural investigation was further conducted by using scanning electron microscopy to reveal the prevalent deformation and strengthening mechanisms. Results obtained by mechanical testing reveal that reduction in tool temperature finally results in the realization of parts with higher strength upon aging. Tool temperatures above 200 °C deteriorate the strength of both alloys, however, improve ductility. Most importantly, the thermo-mechanical process used in the present work has only minor impact on the grain size of both alloys. However, the process appears to have a strong influence on the final morphology and size of precipitates. Elevated tool temperatures and, thus, lower cooling rates, make both alloys prone to the formation of coarse precipitates eventually deteriorating strength.

In this study forming tools temperated at 24 °C and 350 °C were used to systematically investigate the influence of different cooling rates on the mechanical and corrosion properties of a high strength aluminum alloy AA7075 within a novel thermo‐mechanical process that combines forming and quenching simultaneously. The samples formed within heated tools reveal higher ductility and lower material strength compared to the parts processed in cold tools. In addition, the corrosion behavior changed between samples formed with 24 °C forming tools and 350 °C forming tools, respectively. Through cyclic polarization in chloride containing aqueous media a change in the hysteresis and shift of open circuit potential was observed. Metallographic investigation revealed that there was also a very different corrosion morphology for the samples formed within the heated tools. No change in average grain size could be detected but changes of the microstructure in subgrain scale that occur during the forming within the heated tools are responsible for this effect. In further research, the effect of various cooling rates on mechanical and corrosion behavior and the microstructure will be investigated by variation of the forming tool temperature.

Skin-pass rolling is a substantial process step in the production line of sheet material for automotive applications. Textured rolls are used to emboss an immaterial surface structure on sheets for improving their formability in subsequent deep drawing operations. In this paper, state of the art techniques for texturing skin-pass rolls are discussed in order to assess their ability to meet optimal tribological parameters. Two main problems are identified: firstly, structured rolls are affected by ongoing wear limiting the operating time and necessitates perpetual maintenance. Secondly, state of the art techniques are not able to exploit the theoretically known potential of immaterial surface structures for enabling micro-lubrication mechanisms due to geometrical inadequacies.Based on these findings, a new approach for texturing of skin-pass rolls is introduced. The technique uses a localised dispersing of hard ceramic particles by use of pulsed laser radiation. It is shown in this paper that this technique allows the creation of elevated structures with high hardness on the surface of 1.2379 cold-working steel. The wear behaviour of such textured rolls was investigated in a lubricated twin-disc-test. The experiments show that no significant wear of the laser produced structures occur during the test duration. The observed results lead to the assumption that the proposed technique allows the creation of skin-pass roll structures with significantly higher durability.

In this paper the capability of a localized laser dispersing technique for changing the material microstructure and the surface topology of steels is discussed. The laser implantation named technique bases on a discontinuous dispersing of ceramic particles into the surface of steels by using pulsed laser radiation. As ceramic particles TiC, WC and TiB2 are used, substrate material is high-alloyed cold working steel (X153CrMoV12). The influence of the laser parameters pulse length and pulse intensity was investigated in a comprehensive parameter study. The gained surface topology and microstructure were evaluated by optical microscopy, energy dispersive X-ray spectroscopy (EDX) and white light interferometry; mechanical properties were analyzed by micro hardness measurement. The experiments reveal that the alignment of separated, elevated, dome-shaped spots on the steel surface is feasible. The geometrical properties as well as the mechanical properties are highly controllable by the laser parameters. The laser implanted spots show a mostly crack-free and pore-free bonding to the substrate material as well as a significant increase of micro hardness. (C) 2014 Elsevier B.V. All rights reserved.

A simplified approach for the simulation based estimation of the phase distribution in a thermo‐mechanically treated steel component is presented. A key aspect of the approach is the time‐temperature relation for each volume element. Based on a forming simulation with a commercial tool the numerically calculated temperature evolution in the component is analyzed with an in‐house code. The code allows estimating the local phase distribution after the forming process with the help of the continuous‐cooling‐diagram of the material used. A first validation fits well with the existing phase distribution in the component, even though the phase transition in the component is critical in terms of time, deformation and local chemical composition of the material used.

The influence of simultaneously applied mechanical and thermal treatment is used for producing a geometrically complex shaft from 51CrV4 steel resulting in widely differing formations of microstructures. Materials' properties such as internal friction (IF), hardness and electrical resistivity are affected by this change of microstructure formations. The Snoek-Koster peak is identified and analyzed in the actual steel structure.

The CrV-alloyed heat-treatable steel (51CrV4) used for shafts is studied with respect to the influence of different heat treatment and deformation regimes on amplitude (strain amplitude 10−6–10−3) and temperature dependent (293–800K; 1–600Hz) damping. Specimens with different metallographic constituents were measured with and without magnetic field to distinguish between dislocation and magnetoelastic damping. Coercivity of all samples as well as microhardness increases in the order: ferrite–pearlite, as received, bainite and martensite. A clear difference in temperature and amplitude dependent internal friction was detected, too. A Snoek-Köster peak was found to be highest in martensitic state correlating with the dislocation density and reversible relaxation strength. Reversible stress relaxation measurements performed at room temperature from 3s to 1h and at a strain of 2×10−5 led to a reversible relaxation strength of 0.001 for all mentioned metallographic constituents except the martensitic one which was observed to be about four times higher.

对组分梯度功能范围的调整要求已提出,通常通过不同材料组合得以解决.但是这种生产方式一方面需要一系列的工序,另一方面也需要具体的知识,包括所用材料的独特物理及机械特性,尤其是它们的形变及热行为.因此,为了降低能耗,考虑到生态需求,一个组分的现代工业设计程序只应包括一种操作程序和一种具有优化性能的范围大的材料.同时对同质的工件初样进行热处理及机械处理保证了控制材料能够具有最终元件性能的梯度功能.第一步,研究不同热处理对CrV-合金热处理矩形条钢(51CrV4)微观结构演化的影响.生产出只具有铁素体-珠光体、铁素体-珠光体-贝氏体和马氏体结构的条钢.与振动的振幅衰减相关的时间由声学照相机测定.这种声学照相机可以产生彩码声音图谱,显示覆盖于已记录样品图像上噪音的强度和来源.基于作为常规信号处理方法的波束形成概念,该声音分析用来控制换能器阵列上信号的接收或传播方向.条钢的独特微观结构状况造成了振动特性的显著变化.

For the production of bulk steel products with tailored properties, a new approach of thermo-mechanical processing offers a high potential of process innovations. The application of differential thermo-mechanical effects to initial homogeneous workpiece materials combines thermally-controlled material flow with functional grading of mechanical properties. The key effect is the control of local microstructural transformation. The detailed investigation and description of all related phenomena, not only for forming processes of bulk steel products but also for light metals and polymers is the main topic of the recently-established Transregional Collaborative Research Centre 30, which is financed by the German Research Foundation. Recent optimisations of the experimental setup in the field of hybrid metal forming offer new possibilities in the investigation of the main effects. The effects of different heating strategies are investigated through temperature and hardness measurements. Finite element simulations extend the range of the process monitoring. An appropriate choice of differential heating conditions and resulting thermo-mechanical effects creates a functional graded microstructural and resulting mechanical property distribution of bulk products.

Study of anelasticity in AZ31 magnesium-based alloy in initial (hot-rolled at 370 оС) condition and after one and four passes of equal channel angular pressing is carried out. An internal friction peak was found at 170 °C at a frequency f of about 1 Hz. Two possible mechanisms of this peak are discussed: it is suggested that the peak origin is the grain boundary relaxation.

The simultaneous influence of thermal and mechanical treatment was applied to pro- duce a geometrically complex shaft from 51CrV4 steel leading to the formation of microstructures which were significantly different from each other.These microstruc- rural differences were accompanied by a local change of mechanical properties in terms of hardness,electrical resistivity and especially internal friction.The Snoek-K（?）ster peak was recognized and analyzed in the structure of this steel.