Evaluation of Microstructure, Mechanical Properties, Wear Resistance and Corrosion Behaviour of Friction Stir-Processed AZ31B-H24 Magnesium Alloy

In the present investigation, friction stir processing has been done on AZ31B-H24 virgin magnesium alloy. Traversing speed and rotational speed of tool were 20–80 mm/min and 900 rpm, respectively. Microstructure, micro-hardness, wear resistance and corrosion property of processed alloy were investigated. Friction stir processing produced ultra-fine grain of 2.5–3 μm size at weld nugget. Micro-hardness at weld nugget was in the range of 68–72 VHN and became higher than that of the virgin alloy (~ 59 VHN). Maximum tensile strength of ~ 218 MPa, yield strength of ~ 122 MPa, and total elongation of ~ 8.1% were obtained for friction stir-processed magnesium alloy, when produced with 80 mm/min tool traversing speed. Reduction in specific wear rate for all specimens was more than 99% when compared with virgin alloy. The finding was attributed to the change in mechanism of wear from virgin to processed alloy. Micro-cutting/micro-groove formation was evident during wear for virgin alloy; on the contrary, friction stir-processed specimens exhibited micro-ploughing along with wide, blunt, and restricted groove formation. Corrosion resistance of same specimens was reduced as compared to virgin material (~ 0.08 mm/year). Maximum corrosion rate was observed for specimen processed at 80 mm/min tool traversing speed (~ 0.24 mm/year). It is noteworthy that overall corrosion resistance of friction stir-processed alloy was enhanced with decrement in tool traversing speed. At the same time with reference to available literature data, the corrosion resistance of Mg alloy in present experimentation revealed improvement with respect to various Mg alloys, produced through other complementary techniques. The significant improvement in wear resistance along with little reduction in corrosion resistance was attributed to the structural modification of friction stir-processed Mg alloy.