高强铝合金双脉冲VPPA焊缝成形机理

建立双脉冲VPPA(variable polarity plasma arc)焊接系统，进行7A52高强铝合金双脉冲VPPA焊接工艺试验，研究低频脉冲调制叠加高频脉冲对VPPA焊接过程中焊缝成形和焊缝力学性能的影响. 结果表明，低频脉冲周期性振荡液态熔池，可获得表面饱满的鱼鳞纹焊缝；高频脉冲使电弧更为集中，有效地提高了电弧能量密度，穿透力加强；双脉冲耦合振荡加强了对熔池的搅动作用细化了铝合金焊缝晶粒. 焊接接头抗拉强度达到384.13 MPa，相比VPPA焊接接头强度提高了10.21%左右；焊接接头断面收缩率和断后伸长率均有一定程度的提高. 铝合金双脉冲VPPA焊接工艺提高了焊接接头力学性能.

Mechanism of weld formation using double pulsed variable polarity plasma arc welding of high strength aluminum alloy

By setting up a double pulse variable polarity plasma arc welding system, through process test of high strength aluminum alloy welding with double pulse VPPA (variable polarity plasma arc), weld formation and mechanical properties of welded joints of low frequency pulse modulation superposition high frequency pulse were studied. The results show that the low frequency pulse can obtain the fish scales weld by the periodic oscillating liquid molten pool. The high frequency pulse causes the arc more concentrated and improves effectively the energy density of the arc, thus enhance the arc force. Coupled oscillation of the double pulse strengthen the stirring of the molten pool, and refine the grain sizes of the aluminum alloy weld. The tensile strength of welded joints reaches 384.13 MPa, compared with VPPA welded joints, the strength is increased by about 10.21%. And the percentage reduction of area and percentage elongation of welded joints have been improved to a certain degree. The double pulse VPPA welding process improves the mechanical properties of the welded joints of the aluminum alloy.