高强度Al-Zn-Mg合金MIG与CMT+P焊接接头组织及性能研究

Microstructure and properties of MIG and CMT+P welded joint of high strength Al-Zn-Mg alloy

采用熔化极惰性气体保护焊接(MIG)和冷金属过渡+脉冲焊接(CMT+P)两种电弧焊接模式对20 mm厚7A52铝合金进行对比焊接实验,从焊接缺陷、晶粒尺寸及析出相等方面研究不同电弧焊接模式对焊接接头显微组织及力学性能的影响。结果表明,两种焊接接头成形良好且无明显缺陷,焊缝组织为铸态等轴枝晶,并在焊缝中发现条状或块状的富铁杂质相AlFeMn和Mg2Si以及与α(Al)基体呈非共格关系的Al3Mg2相。但MIG焊接焊缝区气孔率为2.73%,而CMT+P焊接焊缝区气孔率仅为0.64%,同时CMT+P模式下焊缝晶粒尺寸较小、热影响区宽度较窄以及晶界偏析较小,因而CMT+P模式下接头强度更高,约为289 MPa。两种模式下拉伸断口均是以韧窝为主要特征的韧性断裂。

Two arc welding modes of melt inert gas welding(MIG)and cold metal transition+pulse welding(CMT+P)were used to weld 20 mm thick 7A52 aluminum alloy.The effects of different arc welding modes on the microstructure and mechanical properties of welded joints were studied from the aspects of welding defects,grain size and precipitation.The results show that the two welded joints are well formed and have no obvious defects.The weld microstructure is as cast equiaxed dendrite.Strip or block iron rich impurity phases AlFeMn and Mg2Si and Al3Mg2 phase with non coherent relationship with theα(Al)matrix are found in the weld.However,the porosity of MIG welding weld area is 2.73%,while that of CMT+P welding weld area is only 0.64%.At the same time,the weld grain size is small,the width of heat affected zone is narrow and the grain boundary segregation is small in CMT+P mode,so the joint strength in CMT+P mode is higher,with about 289 MPa.The pull-down fracture of the two modes is characterized by ductile fracture with dimples as the main feature.