Experimental evaluation of the tool rotation speed and feed rate on micro hardness and microstructure of 5456 aluminum alloy in friction stir welding process

Friction stir welding is a solid state process which is developed by Twi institute in 1991. In present study، lap joint welding of 5456 aluminum alloy sheets were carried out whiles hard working H321 sheet with a thickness of 5 mm was on top of a 2. 5 mm annealed sheet and the simultaneous effect of rotation speed and tool feed rate parameters on microstructure and micro hardness in friction stir welding were investigated. The results show that the friction stir welding causes crush between metal particles، Microstructure homogenization and fine weld beads. The studies showed that increase of rotation speed and reduction of feed rate (increase of welding pitch) causes increase of heat input، vertical flux، grain size and reduction in hardness. With a closer look It was seen that increase in rotation speed from 250 rpm to 750 rpm in constant feed rate and tool angle، increases the grain size from 4. 65 micrometer to 7. 89 micrometer and feed rate with increasing، the grain size reduced from 7. 11 micrometer in speed of 25 mm/min to 4. 77 micrometer in speed of 75 mm/min.