Determining Optimum Friction Stir Weld Variables to Inhibit Abnormal Grain Growth in Al-2195

The objective of this work was to determine the effect of friction stir weld parameters, pin tool geometry, and cryogenic cooling on abnormal grain growth (AGG) in friction stir welded 8.13mm (0.32″) Al-2195. The process parameters, which change the weld nugget microstructure, are varied in the ranges specified according to the predetermined process maps of 2195 Al-Li friction stir welds. The test matrix was comprised 48 six-inch welds using three different pin tools, three weld speeds 76.2, 127, 177.8 mm/min.( 3, 5, 7 in. /min.) three pin rotational speeds (250, 375, 500 RPM), and with or without cryogenic quenching. Cryogenic quenching was accomplished by impinging a liquid nitrogen flow two inches (50.8mm) behind the pin tool during friction stir welding. AGG was initiated by heating and holding the samples at 510 °C for five minutes. In order of significance AGG was avoided or minimized at (1) larger pin shoulder-to-pin diameter tools, (2) low weld speed, (3) higher tool RPM, and (4) cryogenic quenching. The effects of process parameters, tool geometry, and cryogenic cooling on AGG in Al-2195 friction stir welds were analyzed and discussed