Plunge testing to evaluate tool materials for friction stir welding of 6061+20 wt percent Al_2O_3 composite

摘要

A simple plunge test was used to evaluate some of the interactions between 6061 + 20 wt percent Al_2O_3 plates and flat-faced, cylindrical pin tools of H13 steel, WC bonded with 10 wt percent Co, and gas pressure sintered Si_3N_4. The 12.5-mm-diameter pin tools were rotated at 800 rpm under a normal force of 13,344 N and then driven into the plates to a depth of approximately 10 mm. Each test consisted of two segments, a constant-displacement-control plunge to a depth of 1.5 mm followed by a constant-force-control plunge from 1.5 mm to about 10 mm. The forces supported by the pin tools in the constant displacement segments varied with pin tool material. The displacement rates supported by the pin tools in the constant force segment varied with pin tool material. Normal force and spindle torque measurements were used to calculate effective friction coefficients, mu_(eff), for each pin tool material on the 6061/Al_2O_3. These values were: mu_(eff)= 1.024 for the H13, mu_(eff)= 0.768 for the WC10Co, and mu_(eff)= 0.621 for the Si_3N_4. The variations in behavior for the pin tools were attributed to the effect of mu_(eff) on frictional heating. An accumulation of the 6061/Al_2O_3 was found on the H13 pin tool after testing but not on pin tools of the other two materials.