Effect of friction stir processing pass sequence on properties of Mg-ZrSiO4-Al2O3 surface hybrid micro/nano-composites

The present research aimed to fabricate Mg-ZrSiO4-Al2O3 hybrid micro/nano composite on the surface of pure cast magnesium plate by friction stir processing (FSP) route. Then, effect of passes sequence as a new FSP parameter on the maximum temperature experienced by heat affected zone (HAZ), distribution of reinforcements and mechanical properties of the stir zone was investigated. Results showed that temperature of the HAZ was influenced by the number of passes and their sequence. Microstructure observations showed the there exist a uniform distribution of micro-ZrSiO4 and nano-Al2O3 particles after four-passes FSP in the stir zone which improved the hardness of the substrate. However, variations in passes sequence had not considerable effect on hardness distribution. Wear resistance of the composite produced by two passes was higher than the composites produced by four passes with different sequences. The main wear mechanisms were light ploughing due to the three-body abrasion and cracking in the composites produced by two passes while sever ploughing as a result of the two-body abrasion for the four-passes FSPed ones. (C) 2016 Elsevier Ltd. All rights reserved.