铝合金回填式搅拌摩擦点焊组织及力学性能分析

Analysis of microstructure and mechanical properties of refill friction stir spot welded aluminum alloy

采用回填式搅拌摩擦点焊技术对7075-T6铝合金进行了点焊试验.对接头进行了显微组织、显微硬度、剪切和十字形拉伸测试.结果表明,接头显微组织可分为焊核区、热力影响区、热影响区及母材;在焊缝中发现了钩状缺陷、孔洞、未焊合、未完全回填及粘连韧带等缺陷;焊缝区显微硬度呈W形分布,焊点中心呈V形分布;在旋转频率为1 400 r/min,焊接时间为4 s时,接头的抗剪强度达到最大值125.6 MPa,为母材强度的39.6%;接头的十字形拉伸载荷随工艺参数的变化规律比较复杂,最大十字形拉伸强度可达43.9 MPa.

7075-T6 aluminum alloy was successfully spot joined by refill friction stir spot welding process.The microstructure,microhardness,tensile/shear strength and cross-tension strength of the joints were tested.Experimental results indicate that the microstructure can be divided into the nugget zone,thermo-mechanically affected zone,heat-affected zone and base material,respectively.Defects such as hook,cavity,incomplete fusion,incomplete refill and bonding ligament were found in the joint.The microhardness profile in the welded zone exhibited W-shaped appearance,but that in the stir zone exhibited V-shaped appearance.When the rotational speed was 1 400 r/min,the highest tensile/shear strength reached 7 916.0 N,which was 39.6% of the base material.The change of the cross-tension strength with the processing parameters was complicated,and the highest cross-tension strength can reach 43.9 MPa.