材料期刊网

采用搅拌针置中(M4A4)、向镁合金侧偏置2 mm (M6A2)和向铝合金侧偏置2 mm (A6M2) 3种焊接方式, 研究了6 mm厚6061--T651铝合金和AZ31镁合金轧制板材的搅拌摩擦焊接. SEM及XRD分析表明, 3种焊接方式均在焊接界面处发现Mg₁₇Al₁₂相的生成和由于共晶相熔化和随后冷却所形成的孔洞. 在M4A4和M6A2样品中, 少量的Al搅入到镁合金侧形成金属间化合物Mg₁₇Al₁₂, 而在A6M2样品中, 少量的Mg搅入到铝合金中也形成金属间化合物Mg₁₇Al₁₂, 在Mg₁₇Al₁₂与基体的界面处存在微小孔洞. 由于焊核区仅有少量的Mg₁₇Al₁₂生成, 其硬度变化并不显著. 焊接界面处生成的金属间化合物及孔洞显著降低接头的拉伸性能.

Mg alloys are increasingly used in aerospace, aircraft and automotives structures due to the low density and good damping properties, especially, the welding of Mg alloy to Al alloys is of practical importance for widening the application of Mg alloys. Although friction stir welding (FSW) has been used to join Mg and Al alloys, defect free joints are achieved only in the thin plate (less than 4 mm). In this paper, three ways of FSW of 6 mm thick 6061--T651 Al alloy and AZ31 Mg alloy plates, offsetting the pin to the seam between the two plates (M4A4), to the Mg alloy side 2 mm (M6A2) and to the Al alloy side 2 mm (A6M2), were studied. The aim is to examine the effects of the relative position between tool and plate on the microstructure and mechanical properties of FSW Mg/Al alloys joint. SEM and XRD analyses revealed the formations of intermetallics Mg₁₇Al₁₂ and voids in the interface between Mg and Al alloy plates in the three FSW samples. The voids are resulted from the melting and subsequent solidification of eutectic. In the M4A4 and M6A2 samples, some Al are stirred into the Mg alloy side during FSW, forming the Mg₁₇Al₁₂,  whereas in the A6M2 sample, some Mg stirred into the Al alloy side are also transformed to the Mg₁₇Al₁₂. Some fine pores are observed around the Mg₁₇Al₁₂. The hardness of the nugget zone exhibits a slight increase due to the formation of a small amount of Mg₁₇Al₁₂. The intermetallics and pores at the jointed interface decrease the strength of the joints significantly.