OPTIMIZATION OF PULSE FREQUENCY IN PULSED CURRENT GAS TUNGSTEN ARC-WELDING OF ALUMINUM-LITHIUM ALLOY SHEETS

Effects of current pulsation frequency on weld bead microstructure, ha rdness, and tensile properties in AA8090 type aluminium-lithium alloy sheets were studied. It was observed that the structure in the as soli dified weld was predominantly columnar in the case of the conventional (i.e. continuous current) gas tungsten arc welding process. The grain structure became finer and more equiaxed with the introduction of cur rent pulsation. Moreover, there was nit optimum frequency range over w hich the gl ain refinement was a maximum. The same optimum frequency r ange corresponded with maxima in hardness, ultimate tensile strength, and percentage elongation. Tensile strength increased, in general, aft er solution treatment and aging (STA). The best combination of tensile properties was achieved for welds deposited under a 6 Hz pulse freque ncy in the STA condition. (C) 1998 The Institute of Materials.