ذوب جزیی و انجماد مجدد در منطقه ترمومکانیکی حین جوشکاری همزن اصطکاکی نقطه ای آلیاژ AZ۹۱

The present research aims to study the liquation and re-solidification of liquid during friction stir spot welding of AZ۹۱ alloy. Although friction stir spot welding is a solid-state process, the presence of Mg۱۷Al۱۲ intermetallic compounds results in liquation during the welding process. In this study, friction stir spot welding was performed with a tool rotational speed of ۲۵۰۰ rev/min and a tool dwell time of ۵ seconds. The microstructural assessment was carried out by optical and scanning electron microscopes. The results showed that initiation of liquation from the inner and outer edge of the eutectic precipitates occurred based on the melting of residual eutectic. Moving toward stirred zone, a liquid film formed along the grain boundaries. The liquid re-solidified as a composite structure of α-Mg/, which α-Mg phase dispersed in γ-Mg۱۷Al۱۲ matrix. Also, the results showed that eutectic morphology resulting from re-solidification is related to the cooling rate. Eutectic morphology changed from granular to fibrous by increasing the cooling rate. Also, the liquid film along the grain boundaries re-solidified as a divorced eutectic.

Keywords:

Friction stir spot welding , Liquation , Re-solidification , Microstructure. , جوشکاری همزن اصطکاکی نقطه ای , ذوب جزئی , انجماد مجدد , ریزساختار