ZM6 magnesium alloy castings with large size and complex structure are prone to produce defects such as cracks, porosity and inclusions. The development of high-quality welding repair technology will help promote its wider application. In this paper, the argon arc welding technology was used to repair ZM6 cast magnesium alloy with different sizes of circular grooves using optimized pre welding preheating measures, welding process parameters and post welding heat treatment processes. The weld characteristics, microstructure and mechanical properties of argon arc welding repair joints were analyzed. The results showed that for the grooves with diameter of 10~40 mm, the repair welding joint without cracks, pores and incomplete fusion defects was obtained by preheating at 200 ℃ for 1 hour before welding and welding with 160 A current. The grain in the weld area of the repair welding joint was refined, and the grain size was 30~40 μm. The width of the heat affected zone was narrow, but the grains grow and the cluster-like precipitates were significantly reduced. Therefore, the hardness of the heat-affected zone was the lowest. With the increase of groove size, the hardness of weld zone and heat affected zone decreased, and the tensile strength of the sample also decreased. The tensile specimen mainly breaks in the heat affected zone, and the average tensile strength and elongation could reach 93.7% and 95.1% of that of the base metal.
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