Study of the welding procedure for production of Mg alloy joints for practical use

摘要

Based on the welding characteristics clarified in the previous report, the present report investigates a suitable welding procedure for production of good-quality reproducible welds. The deformation characteristics and joint performance obtained with welds produced by the established welding procedure are also examined. The performance of the established welding procedure in the manufacture of light-gauge box-type products seeing strong demand among products using Mg alloys is further investigated. The results obtained may be summarised as follows. 1 During full-penetration butt welding, it is necessary to devise a welding procedure that allows fusion in a short time and involves the application of a backing strip. That is to say, I-butt welding with a root gap is suitable for thin sheets requiring welding at a low welding current, whereas V-butt welding is suitable for medium-thick plates welded under heavy current conditions. In both cases, welding is performed with a continuous supply of small-diameter welding wire. For production of fillet joints, tack welding or full welding without filler metal can be used. During full welding, however, heavy skin roughening occurs under the cleaning effect of the TIG arc. Vertical members are also susceptible to melt-through. To prevent these defects from occurring, it is necessary to perform high-speed welding under heavy current conditions with filler metal. Mg alloys are difficult to form at normal temperature for use in the manufacture of light-gauge products with complex shapes. It is then effective to use a combination of warm working and arc spot welding.