焊接参数对7A04铝合金搅拌摩擦焊接头组织与力学性能的影响

Effect of processing parameters on microstructure and mechanical properties of friction stir welded 7A04 aluminum alloy joints

采用不同的焊接参数对3 mm厚7A04铝合金板进行焊接,并对接头的组织、沉淀相、力学性能及断口形貌进行了分析.结果表明,焊核区组织发生动态再结晶,形成细小的等轴晶粒,热影响区晶粒发生明显粗化.TEM分析结果显示,经搅拌摩擦焊后,焊核区部分沉淀相溶解.焊核区晶粒尺寸随焊接速度增大而减小.当焊接速度为120 mm/min,旋转速度为800 r/min时,接头强度达到最大值454.2 MPa,为母材的95%,断后伸长率为3.97%,为母材的70%.硬度测试显示搅拌摩擦焊接头发生软化,焊缝区域硬度低于母材,硬度值最低点出现在热影响区;拉伸断口形貌SEM图像表明接头断裂方式为韧性和脆性混合型断裂.

7A04 aluminum plates with a thickness of 3mm were welded by friction stir welding( FSW). The microstructure,precipitates mechanical properties and fractured surfaces of the joints were investigated. The results show that the microstructure of the nugget zone consists of fine equiaxed grains due to dynamic recrystallization with precipitates dissolved,and the average grain size of the nugget zone decreases with welding speed increasing. According to the microhardness test,the hardness of the nugget zone is lower than that of the parent material and the lowest hardness locates at HAZ. The ultimate tensile strength( UTS) reaches its peak value( 454. 2 MPa),at a welding speed of 120 mm / min,which is 95% of the parental material. The elongation of the joint is 3. 97% under this parameter.The SEM observed fracture morphologies indicate that the joint fails through a mixture ductile and brittle mode.