温度对AZ31B镁合金扩散连接接头性能的影响

为实现镁合金AZ31 B的可靠连接,根据原子扩散理论,对AZ31 B镁合金进行了扩散连接工艺研究.利用VDW-15型扩散设备,对AZ31B镁合金进行了在不同连接温度条件下的扩散连接.利用金相显微镜、扫描电镜、能谱分析仪器等对扩散连接接头组织及连接界面元素成分进行了分析,测试了接头的剪切强度.结果表明,AZ31B镁合金的...     

保温时间对AZ31B镁合金/铝/铜扩散钎焊接头组织与力学性能的影响

为实现镁合金AZ31B与铜的可靠连接,采用铝作为中间层,在450℃保温30~120min的条件下进行扩散钎焊试验,研究了保温时间对接头组织、显微硬度和剪切强度的影响。结果表明:保温时间为30min时,接头无法实现过渡液相扩散连接;当保温时间为60min时,铝中间层完全溶解,接头中形成了宽约150μm的扩散区,从镁合金侧到铜侧,扩散区的组织依次为镁基固溶体、共晶组织和Cu3Al2Mg2金属间化合物;保温不同时间后,从扩散区的镁合金侧到铜侧,显微硬度均呈阶梯式升高;随着保温时间延长,铜侧过渡层的显微硬度显著增加,接头的剪切强度先增大后降低,并在保温90min后达到最高,为68.2MPa;断裂发生在靠近铜侧的扩散区。     

挤压态AZ61镁合金真空扩散焊接试验研究

采用再结晶退火的方式,细化挤压态AZ61镁合金晶粒,并将细化后的镁合金进行真空扩散焊接研究。剪切强度试验结果表明,在连接压力为10MPa和真空度为18Pa的条件下,扩散温度为470℃、保温时间为90min时可得到最大剪切强度51.95MPa。试验分析表明,扩散温度和保温时间是扩散焊接接头性能的主要影响因素。对扩散焊接头及其周围区域进行显微硬度测量发现,焊缝处的显微硬度最大,偏离焊缝沿母材方向的显微硬度逐渐减小。     

AZ31B镁合金交流电阻点焊接头的力学性能及显微组织分析

采用交流电阻点焊焊接了AZ31B镁合金,研究了点焊接头力学性能的变化规律,分析了点焊接头的显微组织。结果表明:接头抗剪强度随焊接规范呈规律性变化,存在最佳值;表面状态对接头拉剪强度影响很大;接头熔核区显微组织为单一的等轴晶,在α-Mg固溶体的晶界网络处析出β-Mg_(17)Al_(12)离异共晶体;焊点中的裂纹为沿晶热裂纹,断口显现出韧窝沿晶界撕裂的特点。     

连接温度对TA2钛板瞬时液相扩散连接接头组织和性能的影响

利用铜镍锡磷系非晶合金箔作为中间层,使用氩气保护,在不同的连接温度采用瞬时液相扩散焊对TA2钛板进行了连接,并通过光学显微镜、显微硬度仪和材料试验机研究了连接温度对接头组织、显微硬度和剪切强度的影响。结果表明:连接温度低于840℃时,液态中间层等温凝固没有完成,能观察到残留的中间层;随着连接温度的升高,原子扩散加快,残留中间层逐渐减少;870℃时,连接接头组织全部为固溶体;连接温度为850℃时,连接接头具有最高的剪切强度,约为180 MPa。     

Mg/Al合金爆炸焊连接及其界面接合机制

采用爆炸焊接技术制备以AZ31B镁合金为基板,以6061铝合金为覆板的AZ31B/6061合金的层状复合板。对复合板界面的宏观形貌、微观组织、界面元素扩散行为及界面接合性能进行测试、分析。结果表明:AZ31B/6061合金爆炸复合板接合界面呈波状接合;靠近接合界面处的塑性变形程度最大,以孪晶和再结晶形式为主;在AZ31B一侧靠近界面处出现与界面呈45°的绝热剪切带组织,带内为动态再结晶形成的细晶粒组织;接合界面两侧的显微硬度分布为:随着距离接合界面的增大,AZ31B和6061侧的显微硬度值递减趋势;复合板的拉-剪试验结果表明,界面接合强度达193.3 MPa;复合板界面接合机制为压力焊、扩散焊及局部熔化焊综合作用的结果。     

AZ31B镁合金TIG焊焊接接头的疲劳性能

对8 mm厚AZ31B镁合金板及其三种TIG焊焊接接头的静载拉伸性能和疲劳性能进行试验研究。试验结果表明AZ31B镁合金母材的静载抗拉强度为245.50 MPa,TIG焊对接接头、纵向角接接头和非承载十字接头的静载抗拉强度分别为193.55 MPa、229.89 MPa、227.39 MPa。脉动循环(r = 0)疲劳试验表明,在2×106循环次数下,AZ31B镁合金母材的疲劳强度为57.81 MPa,为其静载抗拉强度的23.5％。相同循环次数下,AZ31B镁合金TIG焊对接接头、纵向角接接头和非承载十字接头的疲劳强度为24.60 MPa、20.14 MPa、17.25 MPa,分别为母材疲劳强度的42.6 %、34.8 %和29.8 %。按照国际焊接学会的规范,发现镁合金焊接接头的疲劳级别FAT仅为相应铝合金接头疲劳级别FAT的一半。由此看来,疲劳性能是影响镁合金在承受动态载荷结构中应用的主要因素之一。     

AZ31B镁合金板热成形温度优化及合理温度下成形件的组织与性能

研究了温度对AZ31 B镁合金板显微组织与拉伸性能的影响,分析了不同温度热成形件的成形质量,确定了合理的热成形温度并研究了该温度下热成形件的显微组织与拉伸性能.结果表明:200℃热处理后AZ31B镁合金板能较好地保持细小等轴晶组织,随温度升高,晶粒明显粗化;随温度升高,合金的强度下降而塑性提高,200℃时即可具有良好的...     

基于改进GTN损伤模型的镁合金镦粗成形损伤及裂纹预测研究

镁合金在成形过程中极易产生开裂，精准的损伤预测可以为塑性成形工艺提供理论支撑。为此，基于含连续介质剪切损伤因子的Gurson-Tvergarrd-Needleman(GTN)损伤模型被应用于预测镁合金成形时的损伤演化，通过压缩试样的力-位移曲线标定了AZ31B镁合金的流动应力和剪切损伤参数，预测并验证了AZ31B镁合金在镦粗工艺下的表面损伤及开裂，扩展了模型对低应力三轴度下的成形工艺损伤预测的适用性。在此基础上，对AZ31B镁合金在受压条件下损伤成因、裂纹扩展进行了分析。结果表明，随着压缩位移的增加，镁合金侧面中心区域的切应力不断增加，在此作用下基体内部孔洞沿非垂直压缩方向伸长、聚合，最终形成宏观裂纹；镦粗后的试样侧面裂纹走向与垂直压缩方向所成角度范围为34°～46°，改进的GTN模型模拟结果为44°～54°，原始GTN模型模拟结果均呈90°；改进后的GTN模型可应用于预测镁合金在轧制、热冲压等工艺下的损伤演化行为，为后续工艺优化奠定基础。     

冲击载荷下AZ31镁合金的变形行为和组织演变

利用Hopkinson压杆试验机和限位环限制技术,并通过显微组织观察等研究了AZ31镁合金在动态冲击下的变形行为和组织演变,最后分析了AZ31镁合金的塑性变形机制。结果表明:在1 524~2 024s-1的应变速率范围内,AZ31镁合金的流变应力随着应变的增大而逐渐增大,表现出明显的应变强化效应;随着塑性变形的增加,AZ31镁合金塑性变形机制依次为滑移+孪生、晶粒细化、变形局部化;剪切带内的温升约为241K,达到了孪生动态再结晶的形核温度;晶粒内部的滑移和孪晶转动是剪切带内晶粒细化的主要机制,短暂的温升促进了剪切带内晶粒的细化。     

Eutectic bonding of austenitic stainless steel 316L to magnesium alloy AZ31 using copper interlayer

The eutectic bonding of magnesium alloy (AZ31) to austenitic stainless steel alloy (316L) was performed using pure Cu interlayers. The effect of hold time on the microstructural developments across the joint region and the related effect on bond shear strength were studied at a bonding temperature of 530°C. The bonding process took place through a sequential occurrence of solid-state diffusion of Cu into the magnesium alloy, eutectic phase formation, interlayer dissolution, and isothermal solidification. A (Mg–Cu–Al) ternary intermetallic phase formed within the joint and concentrated into the center of the bond during the solidification stage increasing the hardness value to a maximum average of VHN313 while the maximum recorded bond shear strength was 57 MPa achieving 69% of the AZ31 shear strength and about three to four times of the adhesive joints.     

Developing diffusion bonding windows for joining AZ31B magnesium and copper alloys

In this investigation, Mg–Cu dissimilar materials are joined by diffusion bonding process. The principal difficulty when joining Mg–Cu lies in the existence of hard-to-remove oxide films on the magnesium surfaces and the formation of brittle metallic interlayers and oxide inclusions in the bond region. In this investigation, an attempt was made to develop diffusion bonding windows for effective joining of AZ31B Magnesium and commercial grade copper alloys. Joints were fabricated using different combination of process parameters such as bonding temperature, bonding pressure and holding time. The bonding quality was checked by microstructure analysis and lap shear tensile test. Based on the results, diffusion bonding windows were constructed, and they are presented in this paper. These windows will act as reference maps for selecting appropriate diffusion bonding process parameters to get good quality bonds for Mg–Cu alloys.     

Investigation on overlap joining of AZ61 magnesium alloy: laser welding, adhesive bonding, and laser weld bonding

This paper presents the research on weldability of magnesium alloy AZ61 sheets by overlap laser welding, adhesive bonding, and laser seam weld bonding processes. Microstructures and mechanical properties of the joints are investigated. In overlap laser welding, the joint fractures at the interface between the sheets and maximum shear strength can reach 85% of that of the base metal. Off-center moment during tensile shear test can lead to the strength loss, while the weld edge can also influence the strength as a cracking source. Adhesive bonded joint can offer high tensile shear failure force but low peel strength. Laser weld bonded joint offers higher tensile shear failure force than either laser welded joint or adhesive bonded joint does, and the improved failure load is due to combined contribution of the weld seam and the adhesive. The weld seam can block the adhesive crack propagation, and the adhesive improves the stress distribution, so they can offer a synergistic effect.     

Analysis of the bulging process of an AZ31B magnesium alloy sheet with a uniform pressure coil

As the lightest metal material, magnesium alloy is widely used in the aerospace, automobile, and consumer electronic industries. However, magnesium alloy sheet has poor formability at room temperature. Electromagnetic forming is a high velocity forming technique that can promote the formability of low ductility materials, improve the strain distribution of workpieces, and reduce their wrinkling and springback. In this work, a uniform pressure coil was used to bulge AZ31B magnesium alloy sheets. The finite element method was then used to analyze this bulging process. The bulging contours and displacements of AZ31B magnesium alloy sheets were consistent with the experiment results. The distribution of the magnetic field intensity and magnetic field forces were found to be better than using a flat spiral coil. The deformation rule of AZ31B magnesium alloy sheet using the uniform pressure coil differed from that using the flat spiral coil. The largest strain occurred at the center of the sheet.     

镁合金板带双辊连续铸轧试验研究

在镁合金水平双辊连续铸轧试验过程中,分别施加电磁场、超声波和超声电磁组合场,旨在改善AZ31B镁合金板带的综合力学性能。采用Leica DMI 5000 M金相显微镜、CSS-44100电子试验机和HV-1000硬度试验机等设备检测和分析电磁场、超声波或超声波电磁组合能场处理对AZ31B镁合金板带的微观组织和力学性能的影响。结果表明,常规、电磁场、超声波及超声电磁组合能场铸轧镁板带晶粒平均尺寸(直径)分别为120μm、25μm、27μm及15μm左右;电磁场处理使铸轧镁板带的抗拉强度、屈服强度、伸长率和硬度值比常规铸轧镁板带的分别提高15.7%、24.8%、22.7%和66.6%,超声波处理的分别提高13.8%、26.2%、11.4%和13.4%,超声电磁组合场处理的则分别提高17.1%,27.8%、31.8%和73.8%。这表明在镁合金铸轧过程中施加电磁场、超声波或超声电磁组合场均有利于细化晶粒,改善第二相在枝晶间的分布,提高力学性能,而超声电磁组合场的效果则更显著。同时分析和讨论超声空化效应及电磁效应对镁合金组织细化的作用机制。     

Interfacial Morphology and Bonding Mechanism of Explosive Weld Joints

Interfacial structure greatly affects the mechanical properties of laminated plates.However,the critical material properties that impact the interfacial morphology,appearance,and associated bonding mechanism of explosive welded plates are still unknown.In this paper,the same base plate(AZ31B alloy)and different flyer metals(aluminum alloy,copper,and stainless steel)were used to investigate interfacial morphology and structure.SEM and TEM results showed that typical sine wave,wave-like,and half-wave-like interfaces were found at the bonding interfaces of Al/Mg,Cu/Mg and SS/Mg clad plates,respectively.The different interfacial morphologies were mainly due to the differences in hardness and yield strength between the flyer and base metals.The results of the microstructural distribution at the bonding interface indicated metallurgical bonding,instead of the commonly believed solid-state bonding,in the explosive welded clad plate.In addition,the shear strength of the bonding interface of the explosive welded Al/Mg,Cu/Mg and SS/Mg clad plates can reach up to 201.2 MPa,147.8 MPa,and 128.4 MPa,respectively.The proposed research provides the design basis for laminated composite metal plates fabrication by explosive welding technology.