Surface Engineering of ZE 41 Mg Alloy by Friction Stir Processing: Effect of Process Parameters on Microstructure and Hardness Evolution

Abstract

Abstract Friction stir processing (FSP) is a new solid state processing route that has been attracting the surface engineers to modify the properties of a structure at the surface within the solid state. Modifying the microstructure enhances the material properties which are structure sensitive. Process parameters highly influence the microstructure evolution in FSP. In the present work, ZE41 Mg alloy has been processed by FSP at different process parameters to investigate the effect of process parameters on microstructure evolution and the microhardness. The mechanisms behind the material flow and the formation of new grains during FSP which lead to develop fine grained ZE41 Mg alloy were investigated. Among the nine combinations of tool rotational and travel speeds, combination of 1400 rpm with 25 mm/min was observed as optimum to produce defect free processed zone with higher level of grain refinement. Decreased grain size from 110 µm to 3 µm was observed and an increase of hardness from 60.2 ± 4 to 84.5 ± 5 Hv was also measured at the stir zone after FSP (one pass). The grain size distribution and the hardness distribution were higher when the rotational speed of FSP tool was 1100 and 1800 rpm with 16 and 50 mm/min tool traverse speeds. The level of uniformity was higher with 1400 rpm in the grain size distribution and the hardness. This can be attributed to the difference in the material flow rate and the heat generated in the stir zone. Hence from the present study, it can be understood that uniform grain refinement and increased hardness up to 30% compared with starting value can be achieved in ZE41 Mg alloy by friction stir processing at optimized process parameters of 1400 rpm with 25 mm/min feed without any defect.