APPLICATION OF KEYHOLE AND HEAT-CONDUCTION MODES TO LASER DISSIMILAR METALS WELDING OF MAGNESIUM ALLOY AND STEEL

摘要

The characteristics of welding Mg-alloy to Zn-coatedrnsteel in lap joint configuration by disc laser wererninvestigated. With Mg specimens on the top and arnkeyhole welding mode, two welding runs withrnmoderate energy input were conducted to achievernuniform penetration into the steel specimens withoutrnaffecting the process stability. However, the ensuingrnZn enrichment and the increased thermal stressesrnresulted in cracking at the interface across the Mgrnfusion zone that reduced the joint strength significantly.rnHigh joint strength could be produced when the steelrnspecimens were placed on the top of Mg specimensrnand the process parameters were optimized in a heatconductionrnwelding mode. The Zn-layer wasrncompletely melted at the welded interface andrndissolved the oxide layer on Mg surface. This resultedrnin strong joining between the non-oxidized surfaces ofrnMg and steel. Compared with Zn-coated steel, higherrnjoint strength could be produced between Mg andrnuncoated steel in the case of keyhole welding mode.rnHowever, welding of uncoated steel sheet to Mg platerncould not be achieved with a heat-conduction mode.