第三部分研究了在氦气作保护气体的情况下，用变极性TIG焊方法焊铝时，焊接电流、电弧电压的变化情况和电弧形态的变化。

The third is, when Al is welded by means of VPTIG method of helium, the changes in current, voltage and arc shape.

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探讨了氦气和氩气不同配比对AZ31 镁合金交流钨极惰性气体保护焊（TIG） 焊接性的影响，对不同气体配比的混合气体电弧特性、熔深、焊缝成型进行了分析和测定。

The influence of He-to-Ar ratio in AC-TIG on the AZ31 welding properties was studied. The arc characters, weld penetration, joint forming were measured and analyzed.

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