WARM-TEMPERATURE TENSILE DUCTILITY IN AL-MG ALLOYS

Several binary and ternary Al alloys containing from 2.8 to 5.5 wt pet Mg were tested in tension at elevated temperatures (200 degrees C to 500 degrees C) over a range of strain rates (10(-4) to 2.0 s(-1)). Ten sile ductilities of up to 325 pet were obtained in binary Al-Mg alloys with coarse grains deformed in the solute-drag creep regime. Under te st conditions in which solute-drag creep controls deformation, Mg in c oncentrations from 2.8 to 5.5 wt pet neither affects tensile ductility nor influences strain-rate sensitivity or flow stress significantly. Strength is shown to increase with increasing Mg concentration, howeve r, in the power-law-breakdown regime. The solute-drag creep process, w hich leads to superplastic-like elongations, is shown to have no obser vable grain-size dependence in a binary Al-Mg material. Ternary alloyi ng additions of Mn and Zr are shown to decrease the strain-rate sensit ivity during solute-drag creep, negatively influencing ductility. An i mportant cause of reduced ductility in the ternary alloys during creep deformation is found to be a transition from necking-controlled failu re in the binary alloys to cavitation-controlled failure in the ternar y alloys investigated. An increase in ternary element concentration, w hich can increase the relative volume percentage of proeutectic produc ts, increases cavitation.