Effect of blank holder force control in deep-drawing process of magnesium alloy sheet

A circular cup deep-drawing process was investigated using a magnesium alloy material, which is the lightest practical material for use in manufacturing structural components. An improvement in the limiting drawing ratio (LDR) at 300 °C was observed, by controlling a variable blank holder force (BHF) during the process, in comparison with the constant BHF conditions. The reason for the improvement of the LDR is that the magnesium alloy material has a low F-value, which was obtained from tensile tests when it was warmed to the elevated temperature. When the experimental conditions are not appropriate, such as when BHF is high, the experimentally drawn cup fractured at the wall part (β-rupture). The LDR of the magnesium alloy sheet was improved using the BHF control technique and verified using a finite element method (FEM) simulation. It is confirmed that the FEM simulations behaved in a similar manner to the experiments, with β-rupture being observed during the fracture at the wall part.     

Effects of process parameters on warm and electromagnetic hybrid forming of magnesium alloy sheets

As the lightest structural metal, magnesium (Mg) is attracting increasing interest from both the industrial and academic fields. Magnesium alloy parts are mainly processed by die casting due to their poor sheet formability at room temperature. Warm forming is a popular method of forming; Mg alloy sheets produced in this manner show excellent formability around 200-400 °C. Electromagnetic forming (EMF) can improve the formability of metal sheets without the need for lubricants. In this paper, a new approach, called warm and electromagnetic hybrid forming (WEMF), is presented. The effects of voltage, capacity, and temperature on the bulging height of Mg alloy sheets are investigated. Results show that the bulging height of Mg sheets increases with moderate discharging energies. Enhancing the discharging voltage is also a more efficient method for increasing bulging height compared to simply increasing the capacity. When the discharging energy is kept constant, the bulging height first decreases (<150 °C) and then increases (>150 °C) from room temperature to 230 °C. The formability of Mg alloy sheets improves with increasing temperature, while the forming efficiency of WEMF decreases under similar conditions.     

Preparation and thixoforging of semisolid billet of AZ80 magnesium alloy

Semisolid billet of AZ80 magnesium alloy was prepared by new strain induced melt activated (new SIMA) process and thixoforging experiment was performed. The results show that after as-cast AZ80 magnesium alloy is processed by equal channel angular extrusion, microstructure is refined well due to heavy dynamic recrystallization occurring in severe plastic deformation. Compared with semisolid isothermal treatment and conventional SIMA, semisolid billet with fine and spheroidal grains are achieved in new SIMA. Thixoforging process of semisolid billet prepared by new SIMA has many advantages such as good surface quality of final component, high ability to fill cavity and net-shape. The fine and spheroidal grains and high mechanical properties such as tensile strength of 298 MPa and elongation of 28% can be developed in final part thixoforged.     

Microstructure of ZM6 magnesium alloy with different Nd content

With the purpose of studying the influence of Nd on the alloy structure and castability of ZM6, under the fixed content of Zn and Zr, this paper observes and analyzes the microstructure morphology of ZM6 alloy fracture with different Nd content by the means of uniaxial tension experiment and scanning electron microscope (SEM) observation. The search results indicate that the structure of ZM6 alloy after added Nd can be refined to some extent, while it has no obvious influence on the grain structure and dimension of asast ZM6 alloy. Through increasing the ratio between Nd and Zn, it turns out that Nd and Zn reduces their own solid solubility by each other in a-Mg, and meanwhile, they gather toward the grain boundary, which is beneficial to refine the structure of ZM6 alloy ingot and enables the grain dimension of ZM6 alloy to reach the minimum when the Nd content is 2.5 %. On the basis of the minimization of the grain dimension, the tensile property of ZM6 alloy improves with the Nd content. Thus, it provides theoretical guidance and technical support for the improvement of ZM6 alloy structure.     

模具结构对AZ91镁合金挤压成形性能的影响

AZ91镁合金由于强度高、流动性好等特点,通常用作铸造合金。研究该合金合理的挤压温度、挤压速度及模具结构,对提高其塑性成形性能、开发高强度变形镁合金有重要的理论和实际意义。文章通过热模拟试验研究了AZ91镁合金应力应变关系,确定了最佳变形温度。在此基础上,采用三维有限元法模拟分析了不同挤压速度、模具结构对挤压过程温度场、速度场及应力场的影响。结果表明,采用锥模和流线模时,当定径带长度为15mm~20mm时,可在挤压速度达到5mm/s的条件下成形出表面光滑无裂纹的镁合金棒材;而采用平模挤压时,当定径带长度为10mm~20mm时,获得良好表面质量的挤压速度达到2.5mm/s。在650t的卧式挤压机上,进行了该合金的挤压实验,实验结果与模拟结果相吻合。     

Warm incremental forming of magnesium alloy AZ31

Industrial application of magnesium alloy AZ31 is dramatically increasing due to the very competitive mechanical strength vs. weight ratio. On the other hand, AZ31 is very difficult to be formed at room temperature. In this study incremental forming of the above material is taken into account, with particular reference to formability limits. The role of the main process parameters on material formability was investigated through a wide experimental campaign and a rigorous statistical analysis.     

Prediction of pressure required to extrude a wrought magnesium alloy using optimized strain-dependent constitutive parameters

In the present study, the results of uniaxial compression tests were used to predict the pressure required for extruding a wrought magnesium alloy Mg-Al4-Zn1 under different conditions. The breakthrough and steady-state extrusion pressures were calculated using a strain-dependent constitutive equation and verified by laboratory-scale extrusion experiments. A good agreement was achieved between the calculated and measured extrusion pressure at different ram speeds and reduction ratios for different extrudate shapes. A correlation of the peak extrusion pressure with modified reduction ratio and ram speed was established.     

MB15镁合金板材的超塑性能研究

对轧制态MB15镁合金进行了超塑性能研究 ,在最佳变形温度 340℃ ,应变速率ε· =5 5 6× 10 - 4s- 1时 ,获得应变速率敏感指数m值为 0 5 1,延伸率δ为 4 15 % ,此时流动应力σ仅为11MPa。并分析了在最佳变形温度下应变速率对材料超塑性能及晶粒尺寸的影响     

再生镁合金铸锭质量的控制

介绍了再生镁合金铸锭质量的评价标准,讨论了浇铸参数对镁合金铸锭质量的影响,设计出了镁合金短链铸锭机。通过和镁合金重熔精炼系统配套,镁合金铸锭质量得以提高。     

Cold stamping formability of AZ31B magnesium alloy sheet undergoing repeated unidirectional bending process

The repeated unidirectional bending (RUB) process was carried out on an AZ31B magnesium alloy in order to investigate its effects on the cold stamping formability. The limiting drawing ratio (LDR) of the RUB processed magnesium alloy sheet with an inclination of basal pole in the rolling direction can reach 1.5 at room temperature. It was also confirmed that cell phone housings can be stamped successfully in crank press using the RUB processed AZ31B magnesium alloy sheet. The improvement of the stamping formability at room temperature can be attributed to the texture modifications, which led to a lower yield strength, a larger fracture elongation, a smaller Lankford value (r-value) and a larger strain hardening exponent (n-value).     

镁合金壳体热挤压成形工艺研究

结合非对称锥形壳体零件，研究了镁合金材料MB2的热挤压成形工艺。通过实验研究发现，镁合金材料MB2在适当的温度下，具有较好的成形性。结合理论分析和试验，优化了非对称锥形壳体零件反挤压毛坯和冲头形状，成功生产出合格样件，并进行了小批量生产。     

Broad-beam laser cladding of Al-Si alloy coating on AZ91HP magnesium alloy

In the present study, an attempt was made to improve the wear resistance and the corrosion resistance of AZ91HP magnesium alloy by laser cladding Al-Si eutectic alloy. The results showed that the clad layer mainly consisted of Mg₂Si, Mg₁₇Al₁₂ and Mg₂Al₃ phases. The microstructure of the bonding zone changed from columnar grains to equiaxial grains along the direction of heat-flow. The heat-affected zone consisted of α-Mg and α-Mg + β-Mg₁₇Al₁₂ eutectic. The formation of multiple Mg intermetallic compounds allowed the clad layer to exhibit higher hardness, better wear resistance and corrosion resistance.     

Laser cladding of eutectic-based Ti-Ni-Al alloy coating on magnesium surface

A Ti_70.3Ni_22.2Al_7.5 alloy, optimized from a basic binary eutectic Ti₇₆Ni₂₄ alloyed with different amounts of Al, was laser-clad on AZ91HP magnesium alloy. The coating mainly consists of β-Ti solid solution and Ti₂Ni intermetallic compound resulting in high hardness, good wear resistance and corrosion resistance. The interface between the clad layer and the substrate has a good metallurgical bonding.     

Preparation of semi-solid billet of magnesium alloy and its thixoforming

Preparation of semi-solid billet of magnesium alloy and thixoforming was investigated by applying equal channel angularextrusion to magnesium alloy.The results show that mechanical properties of AZ91D alloy at room temperature,such as yieldstrength(YS),ultimate tensile strength(UTS)and elongation,are enhanced greatly by four-pass equal channel angularextrusion(ECAE)at 573 K and microstructure of AZ91D alloy is refined to the average grain size of 20μm.Through using ECAE asstrain induced step in SIMA and completing melt activated step by semi-solid isothermal treatment,semi-solid billet with finespheroidal grains of 25μm can be prepared successfully.Compared with common SIMA,thixoformed satellite angle framecomponents using semi-solid billet prepared by new SIMA have higher mechanical properties at room temperature and hightemperature of 373 K.     

镁合金手机壳的温热液压成形实验及模拟研究

通过对镁合金手机壳进行温热液压成形实验及有限元模拟,分析了液压加载与冲头运动的不同匹配关系对成形结果的影响,以及成形过程中缺陷产生的原因,并确定了合适的成形工艺参数,即在170℃,控制冲头速度在0.2mm/s~1mm/s,液压载荷不低于5MPa,能一次完成成形底部带斜面,并具有较小圆角半径的镁合金手机壳。液压载荷应在坯料的拉深高度小于3mm时快速的施加,否则,在成形件的底部一平面和斜面与棱边交界处将形成难以消除的堆积缺陷。模拟结果与实验吻合良好。研究表明,温热液压成形可以实现常温或低温液压成形难以实现的复杂镁合金零件成形。     

Electroless Ni-P layer with a chromium-free pretreatment on AZ91D magnesium alloy

A phosphate-manganese conversion film was proposed as the pretreatment layer between Ni-P coating and AZ91D magnesium alloy substrate, to replace the traditional chromium oxide plus HF pretreatment. The subsequent Ni-P deposited on the layer was also characterized by its structure, morphology, microhardness and corrosion-resistance. The pretreatment layer on the substrate not only reduces the corrosion of magnesium during Ni-P plating process, but also reduces the potential difference between the matrix and the second phase. Thus, a Ni-P coating with fine and dense structure was obtained on the AZ91D magnesium alloy, which shows better corrosion resistance than the Ni-P with chromium oxide plus HF as pretreatment.     

镁合金板材胀形和扩孔性能研究

镁合金板由于其具有较小的比重正广泛地应用于零件制造,但它的许多成形性能目前还不能在专业手册中查到,这严重影响了它的成形工艺设计,为此,我们设计了实验模具,并在GB60杯突实验机上对镁合金AZ31板进行了胀形实验和扩孔试验,并对它的成形性能进行了研究,获得了极限胀形系数、平均扩孔率以及成形力与行程的关系曲线等一些有价值的数据,对这一新材料的成形规律有了一定认识。     

Heat treatment of vacuum high pressure die cast magnesium alloy AZ91

Alloys produced by high pressure die casting (HPDC) are generally considered non-heat treatable because trapped gas pores tend to expand, causing surface blistering and bulk distortion. In this paper, vacuum assisted HPDC of magnesium alloy AZ91 was used, and the properties were assessed. The specimens produced using vacuum die casting contain less porosity. Little improvement in yield strength by applying vacuum is found, although a small increase in elongation is observed. A conventional heat treatment applied to the vacuum die cast AZ91 shows pronounced precipitation hardening during aging, especially after a prior solution treatment. However, an associated improvement in yield strength after aging is not observed, and this is related to the decreased contribution of the ‘skin’ effect as a result of grain growth.     

Prediction of knit line formations in complex high pressure die cast magnesium alloy components

Abstract

This work investigates the formation of as cast defects in knit line regions and their effects on local mechanical properties in a thin walled high pressure die cast AM60B magnesium alloy component. The defect distributions and the tensile and bending properties of specimens cut from knit line and other regions are compared. Numerical simulations of the mould filling process, computed X-ray tomography experiments and reports from the literature are used to formulate an initial explanation for the occurrence of metal front dispersion in knit line regions. This is an initial study for a future project investigating knit line formation and process–structure correlations in cast magnesium alloys.