Microstructure and surface mechanical property of AZ31 Mg/SiC_p surface composite fabricated by Direct Friction Stir Processing

Highlights: • A new method of Direct Friction Stir Processing is proposed to fabricate Mg/SiCp surface composite like a planter. • The tool was designed as a hollow and pinless tool, and the reinforcement were preplaced. • The reinforcement particles were homogeneous and dispersed in the stir zone. • The micro-hardness and wear property were promoted by refinement crystallization and reinforcement particles. - Abstract: In this paper, Direct Friction Stir Processing (DFSP) to produce surface composite was proposed. A hollow and pinless DFSP tool was designed to fabricate the surface composite on the AZ31 plate of rolling state. The reinforcement particles flowed out through the through-hole of DFSP tool and entered the enclosed space between shoulder and base metal. They were then pressed into the workpiece as the rotating tool advanced along it just like a 'planter'. Microstructure observed by optical microscope and scanning electron microscope showed that the reinforcement particles were homogeneous and dispersed in the stir zone. The thickness of the composite layer reached 150 μm. The grain size decreased from 16.57 μm to 1.24 μm in the composite layer. The micro-hardness increased from 57.77 Hv to 115.51 Hv. The plow width of the AZ31 with SiC decreased from 620 μm to 410 μm for the wear test