不等厚AZ31B镁合金逆变电阻点焊接头熔核成形及力学性能研究

发布时间：2018-08-10 17:04

【摘要】：镁合金材料具有比强度高、减震性好、易于加工、尺寸稳定及易于回收等优点,逐步取代铝合金在汽车、航空航天、电子等领域的运用,成为实现结构轻量化和材料再利用的理想材料。但在不等厚镁合金板点焊时出现熔核偏移,对接头承载能力有很大影响。因此不等厚镁合金电阻点焊研究,对改善焊接接头质量、提高接头承载能力具有重要的指导意义,并促进镁合金在各领域的广泛应用。本文采用常规点焊、添加不锈钢工艺垫板片、使用不同端面直径的上下电极三种工艺方法,对不等厚AZ31B镁合金板(1.0 mm+0.7 mm)逆变电阻点焊。为了分析焊接工艺对不等厚镁合金板焊接接头质量的影响,以熔核直径、抗剪强度、熔核偏移、表面飞溅等内容作为评判标准进行了工艺试验。试验结果:在薄板镁合金侧添加工艺垫片最佳工艺参数,焊接电流13.3 KA,焊接压力1.7 KN,焊接时间90 ms时,焊接接头最佳抗剪切力达1936 N;常规点焊时,焊接电流22.4 KA,焊接压力1.7 KN,焊接时间100 ms时,焊接接头获得最大抗剪切力达1731 N;对于在薄板侧使用小端面直径(0.6 mm)的电极最佳的工艺参数,焊接电流14.4 KA,焊接压力1.7 KN,焊接时间100 ms时,最大抗剪切力为1594 N。因此在薄板镁合金侧添加工艺垫片获得的焊接接头质量更佳。采用超景深电子显微镜、电子扫描显微镜、X射线衍射仪、显微硬度测试仪等对熔核组织及显微硬度进行分析,研究结果表明:接头熔核的组织主要有柱状树枝晶和等轴树枝晶组成,主要组成相是α-Mg固溶体和晶界上析出的β-Mg17Al12共晶物,熔核柱状树枝晶区和等轴树枝晶区的平均硬度57.84HV、57.82HV高于母材平均硬度值55.44HV,热影响区的平均显微硬度53.94HV低于母材硬度值。镁合金电阻点焊接头受到拉伸载荷呈现有结合面断裂和纽扣式断裂两种断裂方式,两种断裂方式都属于脆性断裂。
[Abstract]:Magnesium alloys have the advantages of high specific strength, good shock absorption, easy processing, stable size and easy recycling. They gradually replace aluminum alloys in automotive, aerospace, electronics and other fields and become ideal materials for structural lightweight and material reuse. The resistance spot welding of magnesium alloys with different thickness has great influence on the welding capacity. Therefore, the research on resistance spot welding of magnesium alloys with different thickness has important guiding significance to improve the quality of welded joints and the load-bearing capacity of welded joints, and promotes the wide application of magnesium alloys in various fields. Methods Inverter resistance spot welding of different thickness AZ31B magnesium alloy sheet (1.0 mm+0.7 mm) was carried out. In order to analyze the effect of welding process on the quality of welded joints of different thickness magnesium alloy sheet, the technological test was carried out with nugget diameter, shear strength, nugget deviation and surface spatter as the evaluation criteria. The optimum process parameters were 13.3 KA welding current, 1.7 KN welding pressure and 90 ms welding time, and the optimum shear resistance of the welded joint was 1936 N. The maximum shear resistance of the welded joint was 1731 N when the welding current was 22.4 KA, the welding pressure was 1.7 KN and the welding time was 100 ms. The best welding parameters are welding current 14.4 KA, welding pressure 1.7 KN, welding time 100 ms, the maximum shear force is 1594 N. Therefore, the quality of welded joints obtained by adding process gaskets on the side of magnesium alloy sheet is better. The results of texture and microhardness analysis show that the microstructure of the joints is mainly composed of columnar dendrite and equiaxed dendrite. The main components are a-Mg solid solution and a-Mg17Al12 eutectic precipitated at grain boundary. The average hardness of columnar dendrite zone and equiaxed dendrite zone is 57.84HV and 57.82HV is higher than 55. At 44HV, the average microhardness of HAZ is 53.94HV, which is lower than that of base metal. The tensile load of resistance spot welding joint of magnesium alloy presents two fracture modes: joint fracture and button fracture, both of which belong to brittle fracture.
【学位授予单位】：太原科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

【参考文献】