Abstract
In the present research, friction stir processing (FSP) of as-cast AZ91-D Mg-alloy has been done to improve its ultimate tensile strength (UTS). Taguchi’s L-9 orthogonal array was used to optimize the process parameters for improving the UTS of AZ91-D parent material (PM). The optimum levels of process parameters were found to be 1000 rpm, 50 mm min^–1 and 6 passes for the rotational tool speed, transverse speed and a number of passes of FSP, respectively. As per ANOVA results, the number of passes has the highest statistical effect of about 41.3 % on UTS.
Additionally, the micro-hardness tests were conducted to confirm the process optimization. The FSPed material with optimized parameters showed an enhancement of 24.56 and 77.5 % in UTS and micro-hardness as compared to PM respectively. The grain size of FSPed material was observed to be 6.88 times lesser than PM. Microstructure evaluation of optimized FSPed material also confirmed the uniform dispersion of β-phase (Mg₁₇Al₁₂) resulting in improved properties.

Key words
magnesium, friction stir processing, Taguchi, tensile strength, micro-hardness, dynamic recrystallization

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