In the lightweight industry, Al–Cu–Mg alloys can be used as an alternative to steel materials and are expected to be widely used in automotive transportation and military equipment. However, hot tearing defects tend to occur easily during the casting process, posing a major challenge to its defect-free casting. In this paper, the effect of cooling rate on microstructure and hot tearing sensitivity of the alloy was studied by using a “cross” hot tearing mold from the perspective of variable cross-section size and mold temperature. The results indicated that with the decrease in cooling rate, the columnar grains of the alloy tended to grow, the dendritic arm spacing increased, and the microstructure of the alloy was coarsened. The cracking susceptibility coefficient (CSC) value of the alloy decreased from 0.675 to 0.476, and the hot tearing susceptibility (HTS1) value reduced from 220 to 12. Therefore, reducing the cooling rate was beneficial to reduce the hot tearing tendency of the alloy. The HTI value and equivalent stress calculated by a commercial simulation software were consistent with the variation law of the HTS1 value and CSC value measured by experiments. The appropriate reduction of the cooling rate promoted the feeding of the residual liquid phase to the hot tearing and prolonged the time of the alloy to release the stress so that the alloy had enough time to relieve the stress through the slip between the grains, thereby reducing the hot tearing tendency of the alloy.

Al-Cu-Mg alloys are highly vulnerable to hot tearing during the solidification process, a phenomenon that severely compromises their mechanical properties and workability, thereby imposing significant limitations on their industrial applications. Therefore, the hot tearing sensitivity of Al-4.4Cu-1.5Mg-0.15Zr-xSm (x = 0.1, 0.3, 0.5 and 0.7) alloys was systematically investigated using a “cross” hot tearing test system. This study delves into the effects of Sm addition on the alloy’s microstructure, second-phase distribution, solidification behavior, hot tearing sensitivity, and the underlying hot tearing mechanism. A comprehensive analysis was conducted to clarify the role of Sm in regulating hot tearing susceptibility during solidification, combining microstructural characterization with thermodynamic solidification behavior analysis. The results indicate that the d-value, HTS1 and CSC values decrease initially and then increase with the Sm content increase. When the Sm content is 0.5 wt.

In this paper, the effects of grain size, precipitated phases, and texture components on the hoop mechanical properties of GH4169 thin-walled tubes were investigated. The hoop mechanical properties were measured using hoop tensile experimental setup combined with digital image correlation (DIC). Based on the theoretical calculations, the hoop stress-strain curve of GH4169 thin-walled tubes was obtained. As the annealing temperature increased, the delta phase gradually dissolved, and the grain size increased from 19.06 to 51.31 mu m. This resulted in the weakening of both grain boundary strengthening and precipitation strengthening, thereby reducing the strength of the tube. Concurrently, the hindering effect on dislocation slip weakened, causing the elongation to increase. Over the annealing temperature range of 960-1040 degrees C, the yield strength decreased from 310.3 to 231.2 MPa, the tensile strength decreased from 625.2 to 528.7 MPa, and elongation increased from 29.8 % to 40.4 %. Notably, at an annealing temperature of 980 degrees C, the n value of the tube achieved its maximum value of 0.338, which was influenced by the precipitated phases and texture. At annealing temperatures of 960 degrees C and 980 degrees C, the texture components of the tubes were mostly random textures with low texture intensity. As the annealing temperature increased, the texture intensity of the tubes increased, and the preferred orientation became obvious. In particular, at an annealing temperature of 1000 degrees C, Copper texture exhibited high texture intensity. At 1040 degrees C, the F texture and R texture also developed significantly. The reduction in the n value of the tube could be attributed to the F texture, Copper texture, and precipitated phases.

In this work, the Al-Cu-Mg alloy with different Y (0-0.2 wt%) and Ce (0.5-1.5 wt%) are designed. The effect of mixed addition of Y and Ce on the grain structure and hot tearing for Al-4.4Cu-1.5Mg-0.15Zr alloy was investigated using "cross" hot tearing mould. The results indicate that as rare earth Y and Ce increases, the grain size becomes finer, the grain morphology changes from dendrite to equiaxed grain, and effectively reduce the hot tearing sensitivity coefficient (HTS1) and crack susceptibility coefficient (CSC) of the alloy. With the increase of Ce element (0.5-1.5 wt%), the hot tearing susceptibility of the alloy decreases first and then increases. With the increase of Y element (0-0.2 wt%), the hot tearing sensitivity of the alloy decreases. When the content of rare earth is 0.2 wt% Y + 1.0 wt% Ce, the minimum HTS1 value and CSC value of the alloy are 68 and 0.53, respectively. Rare earth Ce refines the alloy microstructure, shortens the feeding channel, and reduces the hot tearing initiation. Meanwhile, the rare earth Y can form Al6Cu6Y phase at the grain boundary, improve the feeding capacity of the alloy. Therefore, appropriate addition of rare earth Y and Ce can effectively reduce the hot tearing tendency of the alloy.

The intermetallic compound and hot tearing sensitivity of Al–4.4Cu–xMg–0.15Zr (x = 1.0–2.5 wt

The present work focuses on the mechanisms of liquid film feeding and intermetallic compounds interface property in the Mg content of Al–Cu–Mg alloys hot cracking behavior. Experimental results reveal that two types of hot cracking microstructure are observed when the mushy zone of Al–Cu–Mg alloys is constituted of liquid film and spherical solid grains. One type is attributed to the premature formation of a closed region which prevents the feeding of the liquid film and insufficient feeding of the liquid film, while the other is formed due to unstable intermetallic compounds. Combined with multiscale simulation calculations, it is demonstrated that in alloys which hot cracking is induced by the formation of a premature closed zone and insufficient liquid film feeding, the Al–4.0Cu–1.5Mg alloy exhibits the highest residual liquid film feeding volume (Vresidual*) value of 5.59 × 104 µm3, indicating the lowest hot cracking susceptibility. Therefore, in the absence of dendrite bridging effects on hot cracking formation, the mechanism by which grain refinement affects hot cracking is to decrease the solid phase shrinkage volume (Vs*) while increasing the liquid film feeding volume (Vfeeding*), thereby reducing the tendency for hot cracking initiation. Furthermore, molecular dynamics (MD) simulation is used to calculate the interface stability of different intermetallic compounds. The results demonstrate that the interfacial separation works for Al2CuMg//Al and Al2CuMg//Al2Cu are 28.805 and 2.849 J/m2, respectively. These values are higher than those for AlCuMg//Al and AlCuMg//Al2Cu (26.939 and 2.473 J/m2), indicating that interfaces with AlCuMg as the matrix are more susceptible to be separated. When the Mg element content exceeds 1.5 wt pct, the formation of the unstable AlCuMg phase increases the sources of hot cracks. The research findings of this work provide design insights and theoretical guidance for development alloys with low hot cracking susceptibility.

Herein, a hot cracking initiation criterion based on the characteristics of solidification liquid film and the microstructure was proposed, which integrated both the mechanical and non-mechanical factors during solidification. The criterion also took the effect of the shrinkage volume of the solid–liquid two-phase in the mushy zone, the flow behavior of the liquid film and the microstructure on the feeding behavior into account. Meanwhile, the effect factors of hot cracking initiation such as alloy composition, microstructure, mold design and process condition were included in this criterion, and it could quantitatively calculate whether hot cracks occurred under a certain state or not during solidification. The criterion was utilized to predict whether hot cracks occurred in Al-4.0 wt

Hot tearing is one of the most serious defects during the casting solidification process. In this study, a new type of multichannel “cross” hot tearing device was designed. The hot cracks initiation and propagation were predicted by the relationship between temperature, shrinkage force and solidification time during the casting solidification process. The reliability and practicability of the multichannel “cross” hot tearing device were verified by casting experiments and numerical simulations. The theoretical calculation based on Clyne-Davies model and numerical simulation results show that the hot tearing tendency decreases in the order: 2024 Al alloy>Al-Cu alloy>Al-Si alloy at a pouring temperature of 670 °C and a mold temperature of 25 °C. Feeding of liquid films at the end of solidification plays an important role in the propagation process of hot tearing. The decrease of hot tearing tendency is attributed to the feeding of liquid film and intergranular bridging.

In this study, Al–4Cu alloy specimens with spherical grains and liquid films were obtained by isothermal reheating treatment. The hot cracking of the solidification process was determined using a modified constrained rod casting experimental apparatus, and the effect of liquid film characteristics at the end of solidification on hot cracking initiation of Al–4Cu alloys was systematically investigated by combining molecular dynamics simulations and other methods. With the extension of soaking time, the liquid fraction (liquid film fraction at the end of solidification) and grain shape factor increased with higher isothermal reheating temperatures. Additionally, the widened filling channel decreased the hot cracking initiation temperature and the critical hot cracking shrinkage stress was found to increase, thus reducing the hot cracking severity in Al–4Cu alloys. Molecular dynamics simulations revealed that with the extension of soaking time, the composition of the liquid film changed at different isothermal reheating temperatures, but the short-range structure and atomic ordering of the liquid film remained the same. The activity of the liquid film increased in equilibrium, leading to a decrease in viscosity and an increase in fluidity, which contributed to the filling behaviour. After isothermal reheating at 640 °C for 60 min, the liquid fraction reached the maximum, and the viscosity of the liquid film was the minimum. In addition, almost no hot cracks were found.

The effect of rare earth Ce on the hot tearing sensitivity of the Al-Cu-Mg-Y alloy is studied by using a self-made multi-channel "cross" hot tearing test device. Based on hot tearing sensitivity, solidification temperature, shrinkage force and microstructure of the as-cast Al-4.4Cu-1.5Mg-0.15Zr-0.15Y alloy with different contents of Ce, the influence regularity and mechanism of rare earth Ce on the hot tearing are systematically studied. The results show that the hot tearing resistance of the alloy is evidently improved due to grain refinement and the increase of feeding capacity of liquid phase in the later stage of solidification with addition of Ce. The average grain size, the HTS 1 value and the CSC value of the alloy firstly decrease and then increase with the content of Ce increases from 0 to 2.5 wt.%. Compared with the alloy without Ce, the average grain size of the alloy with addition of 1.0 wt.% Ce reduces from 150.04 to 90.23 μm. The fluidity and hot tearing resistance of the alloy are significantly enhanced owing to the generated Al 8 Cu 4 Ce phase. Furthermore, when the Ce content exceeds 1.0 wt.%, which leads to the microstructure coarsening and the rise of the hot tearing sensitivity of the alloy compared with addition of 1.0 wt.%.

选取Al-4.4Cu-1.5Mg-0.15Zr合金,分别添加(质量分数)0.1％的Pr、0.1％的Sm、0.1％的Y,利用SEM、EDS、XRD等分析方法研究稀土元素对合金的作用机理.结果表明,分别添加0.1％的Sm、Pr、Y后,与基体合金相比,合金组织得到不同程度的细化,二次枝晶间距减小,合金中孔洞等缺陷减少;稀土元素分别在晶界处,形成Al3Pr、Al10Cu7 Sm2、Al6 Cu6Y相;添加0.1％的Pr,合金组织细化效果最佳,二次枝晶的间距最小,稀土化合物在晶界处分布最均匀.

In this study, the molecular dynamics (MD) calculation method was used to calculate the diffusion coefficient of solute atoms in the liquid film (LF) at the end of solidification, and the effect of constitutional supercooling in LF on the hot cracking tendency of Al-4.0 wt% Cu alloy was investigated combined with experiments. The MD calculation result indicated that the diffusion coefficient of Cu elements (DL) increased as the atomic percentage of that in the LF decreased at a specific temperature within the solidification range (620 degrees C was chosen in this study). Supercooling degree produced by constitutional supercooling (Delta Tc) decreased while the constitutional supercooling zone width (Delta x) increased with DL, which facilitated extending the LF complementary shrinkage zone during solidification, and cellular grains easily formed after solidification, thus reducing the hot cracking tendency of Al-4.0 wt.%Cu alloy. The experimental results concluded that the hot cracking tendency of Al-4.0 wt. %Cu alloy decreased as the atomic percentage of Cu elements in the LF decreased, which verified the accuracy of the MD calculation results.

In this study, the effect of Pr element on the microstructure and the hot tearing sensitivity of the Al-4.4Cu-1.5Mg-0.15Zr alloy was studied by using a self-made multi-channel 'cross' hot tearing test device. The result showed that as the content of Pr increased from 0wt.% to 0.5wt.%, the average grain size, the HTS1 value and the CSC value of the alloy firstly reduced and then rose, and the range of the solidification temperature firstly decreased and then increased slightly. Compared with alloy without Pr, the average grain size descended from 168μm to 86μm, the range of the solidification temperature decreased from 143.71°C to 137.90°C, the HTS1 of the alloy decreased from 228 to 60, and the CSC value declined from 0.629 to 0.159 with addition of 0.3wt.% Pr. The mechanism of reducing the hot tearing sensitivity of the alloy with addition of Pr element was obtained that the microstructure was refined and the solidification temperature range was decreased, which were conducive to the formation of more intergranular bridging at the grain boundary, finally the hot tearing sensitivity of the alloy was reduced.

为了研究室温条件下6016-T4铝合金板材的高应变速率变形行为,采用分离式霍普金森压杆(SHPB)设备进行应变速率为1600、2300和3200 s-1的压缩变形实验,建立描述材料变形行为的Johnson-Cook本构模型,应用ABAQUS软件进行热力耦合仿真模拟,研究实验过程中合金的变形和温度场变化规律.结果表明:在6016-T4铝合金板材室温高应变速率压缩变形过程中,当应变速率较高时,合金表现出负应变速率敏感性;通过Johnson-Cook本构模型计算出的数据与实验数据吻合良好;通过仿真模拟可知,合金内部的温度明显升高且分布不均匀,绝热温升对合金变形产生了一定的软化作用.

In this paper, the effect of Y content on hot tearing properties of cast Al–Cu–Mg alloy was studied. The effect and mechanism of Y on hot tearing of cast Al–4.4Cu–1.5Mg–0.15Zr alloy were studied by analyzing the microstructure evolution, phase structure, solidification process and hot tearing sensitivity coefficient of the alloy with different Y additions, and determined the appropriate amount of Y element. The results showed that Y improves hot tearing resistance of Al–4.4Cu–1.5Mg–0.15Zr alloy by refining microstructure and reducing the solidification temperature range. The suitable amount of Y is 0.15 wt%. At this time, a certain amount of Al6Cu6Y low melting point phase is formed in the alloy, and the grain structure is the smallest, which significantly improves the hot tearing resistance of Al–4.4Cu–1.5Mg–0.15Zr alloy. The microstructure coarsening and hot tearing tendency increase with increasing Y content. The experimental results are basically consistent with the hot tearing sensitivity predicted by the Clyne–Davies model.

Ni-based alloy was surfaced on low-carbon steel by plasma arc surfacing under DC transverse magnetic field.The hardness,wear resistance,microstructure and phase constitution of the surfacing layers were investigated via hardness and wear tests as well as SEM,EDS and XRD analysis.The influence of DC transverse magnetic field on the microstructures and wear resistance of the surfacing layer,the shape and amount of the hard phase were systematically studied.Furthermore,preliminary analysis and discussion of the DC transverse magnetic field mechanism were made.The results show that the optimal properties are obtained when surfacing current and magnetic field current matches properly.When the surfacing current is 140 A and the magnetic field current is 2 A,the hardness and the wear loss of surfacing layer are 66.3 HRC and 0.0767 g,separately.At the point,the amount of hard phase is the most and the distribution of hard phase is even,the comprehensive mechanical properties of surfacing layer are enhanced.

In order to improve the properties of surfacing layers,study the influence of surfacing current and magnetic field current on properties and microstructure of surfacing layer,DC transverse magnetic field was applied when Co-based alloy was welded on the surface of low-carbon steel by plasma surfacing.The hardness,wear resistance,microstructure and phase constitution of the surfacing layers were investigated via hardness and wear tests as well as SEM and XRD analysis.Furthermore,the influence of surfacing current and magnetic field current on the hardness and wear resistance of the surfacing layer were studied.The results showed that the properties of surfacing layers with introducing DC transverse magnetic field were better than that without magnetic field.When the surface current was 160 A and the magnetic field current was 3 A,the optimal effect of grain refining could be gained.The optimal hardness and wear extent have been obtained at the same time.Furthermore,the DC transverse magnetic field can suppress the arc blow and improve the stability of surface process.

In order to systematically study the influence of surfacing current and magnetic field current on hardness and wear resistance of surfacing layer, longitudinal DC magnetic field was applied during plasma arc surfacing Co-based alloy on low-carbon steel. The hardness, wear resistance, microstructure and phase constitution of the surfacing layer were investigated through the tests of hardness, wear, SEM and XRD analysis. The results show that the surfacing current and magnetic field current must be matched properly to achieve the optimal properties of surfacing layer. The optimal values are obtained when the surfacing current is 160A and the magnetic field current is 3A, where the hardness is 43.7 HRC and the wear loss is 0.5493g. The proper electromagnetic stirring induced by electromagnetic field can not only refine the microstructure but also improve the hardness and wear resistance of the surfacing layer.

In order to study the weldability of AZ31 magnesium alloy,AC tungsten inert gas welding (TIG) was conducted for the AZ31 magnesium alloy plate. The microstructure of the welding seam was analyzed using x-ray diffractometer,scanning electron microscope and optical microscope. In addition,the hardness and ultimate tensile strength of the samples obtained with different welding current were determined. The results show that with an increase in welding current,the formability of welding seam becomes worse and the grains get coarsed. At the same time,both gas porosity and crack are easy to generate,which will reduce the properties of the joint. The microstructure of the welding seam is composed of α-Mg matrix and β-Al12Mg17phase. It is also noted that the welding current significantly influences the shape of molten pool and the welding quality of welding joint.

In order to improve the properties of surfacing layers,study the influence of magnetic field on microstructure and properties of carbon arc surfacing layer,a DC transverse magnetic field was applied to the carbon arc surfacing of Cr-B-Ni-V iron based alloy system.An attempt to refine the structure of surfacing layer metal and control the morphology and distribution of hard phase in surfacing layer was made.The influence of surfacing current and magnetic field current on degree of hardness and wear resistance was obtained through hardness test,wear test and microscopic test.The results show that the surfacing layer of introducing magnetic field has higher hardness and better wear resistance than the surfacing layer without magnetic field;The properties of surfacing layer are optimal when surfacing current and magnetic field current match each other.That is,the hardness and wear resistance of surfacing layer are optimal when surfacing current is 180A and magnetic field current is 3A.At this point,the hard phase in the surfacing layer is fine and even,hexagonal in shape,the orientation of which is consistent.