【摘要】 对两层两道MIG焊接的6005A铝合金型材与5083铝合金板材焊接构件进行取样,详细研究了焊接接头部分熔化区(PMZ)的微观组织特征,重点分析了6005A铝合金型材挤压成形坡口附近原始微观组织对PMZ中发生的晶界液化行为的影响。研究发现,在焊接接头的PMZ观察到了与母材坡口处微观组织存在明显相关性的晶界液化特征。由于6005A铝合金型材挤压成形的坡口表层存在厚度约为1 000μm～3 000μm的粗晶层,且第一道次焊缝稀释率较低,第二道焊缝的稀释率较高,因此在PMZ I(第一道焊缝的PMZ)中观察到的连续分布的粗晶组织和在PMZ II(第二道焊缝的PMZ)局部观察到粗晶组织均为残留的焊接坡口粗晶层组织。进一步的分析表明,PMZ粗晶区晶界液相主要来源于熔池金属的沿晶渗透;近缝细晶区晶界液相的来源既有熔池金属的沿晶渗透,又有晶界低熔点共晶组织的熔化;低熔点共晶组织熔化是距熔池稍远的细晶区发生晶界液化的主要机制。5083铝合金板材坡口附近的原始组织呈细小纤维状组织特征,在5083铝合金侧的PMZ观察到了液相沿拉长晶粒的边界液化的特征。更多还原

【Abstract】 Joint samples were taken from the welding part of 6005 A aluminum alloy-profile and 5083 plate welded by melt inert-gas welding(MIG) using the two-layer two-pass welding process. The microstructure characteristics of the partial melting zone(PMZ) of the welded joint were studied in detail. The effect of the original microstructure near the groove on the grain boundary liquation in the PMZ was analyzed and discussed. The research shows that the grain boundary liquation characteristics in the PMZ are significantly correlated with the original microstructure of the welding groove. There is a coarse-grained layer with thickness of 1 000-3 000 μm on the extruded welding groove surface of 6005 A aluminum alloy profile, and the dilution rate is low for the first pass weld and high for the second pass weld, thus the continuously distributed coarse-grained structure observed in PMZ I(PMZ of the first pass weld) and the isolate coarse-grained structure observed in the local part of PMZ II(PMZ of the second pass weld) were considered as the retained grain structure of the welding groove. Further analysis shows that the liquid phase at the grain boundary in the coarse-grained zone of PMZ is mainly originated from the intergranular penetration of the the weld metal, and the source of liquid phase at the grain boundary in the fine-grained zone near molten pool is from both the intergranular penetration of the molten pool metal and the melting of the low melting point eutectic structure at the grain boundary. Additionally, the melting of the low melting point eutectic structure is the main mechanism of the grain boundary liquation in the fine-grained zone slightly away from the molten pool. Moreover, the original microstructure of the welding groove of 5083 aluminum alloy plate is characterized by fine fibrous structure, and liquation along the elongated grain boundary was observed in the PMZ on the side of 5083 aluminum alloy.更多还原