AZ31镁合金TIG焊接工艺及接头应力腐蚀行为研究

发布时间：2018-06-13 03:04

本文选题：AZ31镁合金 + 钨极氩弧焊　；参考：《西华大学》2015年硕士论文

【摘要】：本文采用钨极氩弧焊(TIG)对2mm厚的AZ31变形镁合金进行焊接,优化其焊接工艺参数;探讨慢应变速率对焊接接头力学行为的影响规律;对焊接接头的腐蚀性以及不同介质下应力腐蚀敏感性进行研究。研究表明:AZ31镁合金焊接接头由母材(BM)、热影响区(HAZ)及焊缝(WZ)构成,其中母材和热影响区组织为α-Mg单相固溶体,焊缝组织为α-Mg固溶体和弥散分布的β-Mg17Al12金属间化合物。随着电流增大,焊缝区β-Mg17Al12金属间化合物增多,热影响区晶粒变大,抗拉强度先增大后减小。综合分析,电流在90A时焊接接头力学性能最佳,抗拉强度为223MPa,可达到母材抗拉强度的89.2%,断裂发生在热影响区,断裂方式为韧-脆混合断裂。AZ31镁合金焊接接头在不同应变速率下表现出正应变速率效应,随着应变速率减小,强度减小,延伸率增加,塑性变形能力增强;AZ31镁合金焊接接头发生塑性变形的主要方式是孪生,随着应变速率的减小,焊接接头孪晶增多,晶粒变小,且接头晶粒取向发生变化,晶粒在{000 2}晶面上有择优取向;不同应变速率下焊接接头断口缩颈较母材小,断裂方式均为韧-脆混合断裂,随着应变速率减小韧性特征明显。AZ31镁合金焊缝耐腐蚀性能明显优于母材和热影响区,其中热影响区耐腐蚀性最差;在3.5wt.%NaCl、3wt.%NaCl+0.5wt.%H2O2及3.5wt.%NaCl+2wt.%KCrO4溶液中焊接接头失效部位均在热影响区,且无明显塑性变形,抗拉强度为惰性介质中的50%左右,断口较平整、截面存在多条主裂纹并伴有分叉现象;焊接接头在三种溶液中应力腐蚀指数ISSRT较母材大,其中在3.5wt.%NaCl+2wt.%KCrO4溶液中最大为0.61。
[Abstract]:In this paper, tungsten arc welding (TIG) is used to weld 2mm thick AZ31 deformed magnesium alloy, and its welding parameters are optimized. The influence of slow strain rate on the mechanical behavior of welded joint is discussed. The corrosion of welded joint and the stress corrosion sensitivity under different medium are studied. The research shows that the welding joint of AZ31 magnesium alloy is from the parent material (B M), heat affected zone (HAZ) and weld (WZ) structure, in which the parent material and the heat affected zone are composed of alpha -Mg single phase solid solution, the weld structure is alpha -Mg solid solution and diffusion distributed beta -Mg17Al12 intermetallic compound. With the increase of current, the intermetallic compound of the weld zone is increased, the grain of the heat affected zone becomes larger, the tensile strength increases first and then decreases. When the current is at 90A, the mechanical properties of the welded joint are the best, the tensile strength is 223MPa, which can reach 89.2% of the tensile strength of the parent material. The fracture occurs in the heat affected zone. The fracture mode is the ductile brittle mixed fracture.AZ31 magnesium alloy welded joint with the positive strain rate effect at different strain rates. With the decrease of the strain rate, the strength decreases and the strength decreases. With the increase of elongation and the increase of plastic deformation ability, the main mode of plastic deformation in AZ31 magnesium alloy welding is twin. With the decrease of the strain rate, the twin grains are increased, the grain size becomes smaller, the grain orientation of the joint is changed, the grain is preferred on the {000 2} crystal surface, and the fracture necking of the welded joint at different strain rates is more than the mother. The fracture mode is both toughened and brittle fracture. The corrosion resistance of.AZ31 magnesium alloy welds is obviously better than that of the parent material and heat affected zone with the decrease of the strain rate. The corrosion resistance of the heat affected zone is the worst, and the welding joint failure parts in 3.5wt.%NaCl, 3wt.%NaCl+0.5wt.%H2O2 and 3.5wt.%NaCl+ 2wt.%KCrO4 are all in the heat shadow. There is no obvious plastic deformation, the tensile strength is about 50% in the inert medium, the fracture surface is more than 50%, and there are many main cracks and bifurcation in the cross section. The stress corrosion index of the welded joint in three kinds of solution is larger than that of the parent material, and the largest is 0.61. in the 3.5wt.%NaCl+2wt.%KCrO4 solution.
【学位授予单位】：西华大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG444.74;TG172.9

【相似文献】