Formation Mechanisms Of Snowflake-like Defects On Turned Surface Of ZL101Al-Si Cast Alloys

The casting Al-Si alloy has the advantages of low density and high specific strength.And it has many excellent properties, such as casting property, anticorrosion, weldability.It is widely used in the industry of aerospace, automobile, instrumetation, etc. Thecasting Al-Si alloy is also widely used in high voltage switch. High voltage switchequipment’s shell belongs to complex castings, higher requirements on the materialproperties and the forming technology. Not only to ensure that the shell of high strength,but also to ensure its corrosion resistance, airtight performance, thermal crackingresistance and oxidation resistance.Turning the Al-Si alloy resolved parts, the turned surfaces produce snowflack-likedefects, affect workpiece operational performance. In order to find the snowflack-likedefects generation mechanism, the paper carried roughness measurement on the ZL101castings machined surface, and mechanical properties and microstructure observation onthe position of castings machined surface’s snowflack-like defects and no snowflack-likedefects.The results show that the roughness of turning workpiece surface’s snowflack-likedefects position is significantly higher than no snowflack-like defects position; thestrength of the sample is less than the position of no snowflack-like defects.Microstructure observation show that the position of snowflack-like defects samples’α-Al phase crystal grain size and dendrite arm spacing are significantly higher than theposition of no snowflack-like defects, and the position of eutectic silicon phase particlesize and the proportion of eutectic organization are higher than the position of nosnowflack-like defects. Coarse microstructure and eutectic organization’s increase areprompted the formation of snowflack-like defects on Al-Si alloy surface during turningprocess.With the casting thickness increases, cooling rate gradually decreases, undercooling gradually decreases, and many eutectic organizations are distributed in the interdendritic.The castings of small cooling rate are easy to generate snowflack-like defects, while thecastings of big cooling rate are difficult to produce snowflack-like defects. Therefore, byimproving the casting process, increasing the cooling rate of the casting, it can reduce oreliminate snowflack-like defects during the turning process.