铝合金因其密度低,比强度高等特性,被广泛应用到航空航天、军事工业等领域.与其他焊接工艺相比,变极性等离子弧焊接在大型铝合金结构件加工方面具有突出优势.针对轻金属合金等离子弧焊接过程中匙孔难以自由闭合的问题,提出了气电分离时序脉冲等离子弧环焊缝收弧方法,对比研究了环焊缝收弧方法与手工钨极惰性气体保护焊(tungsten inert gas welding,TIG焊)填补法焊缝匙孔闭合处的微观组织与力学性能.结果表明,通过调节焊接起弧、收弧策略,实现了等离子弧匙孔自由闭合,焊缝收弧区成形良好,组织为均匀的等轴晶;抗拉强度为329.9 MPa,断后伸长率为 16.3%,比TIG填补法的抗拉强度提高了 22.91%,断后伸长率提高了 55.24%.平均硬度值为78.9 HV0.2,热影响区硬度呈下降趋势,熔合线处硬度呈升高趋势,焊缝区硬度波动范围为75～81 HV0.2.
Microstructure and mechanical properties of welds at key-hole closures in variable-polarity plasma arc welding of Al alloy
Al alloy is widely used in aerospace,military in-dustries,and other fields due to its low density and high specif-ic strength.Variable polarity plasma arc keyhole welding is a preferred method for processing large aluminum alloy structur-al components.However,keyhole closure is a challenge in plasma arc welding of light metal alloys.To address this issue,a gas-electric separation timed pulse plasma arc ring welding method named keyhole self-closing method is proposed.The microstructure and properties of the keyhole closure in the ring welds by the proposed method and the manual TIG welding filling method was compared.The results demonstrate that by adjusting the welding arc starting and ending strategies,the keyhole closure was achieved,with the formation of well-shaped weld joints exhibiting a uniform equiaxed crystal mi-crostructure.The tensile strength was about 329.9 MPa,with an elongation of 16.3%,representing a 22.91%increase in tensile strength and a 55.24%increase in elongation compared to the keyhole filled by the TIG welding.The average hard-ness value was 78.9 HV0.2,with the heat-affected zone show-ing a decreasing trend in hardness,the fusion line exhibiting an increasing trend,and the weld zone hardness fluctuating in the range of 75 to 81 HV0.2
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