INFLUENCE OF PULSE PARAMETERS ON SOME MECHANICAL _ PROPERTIES OF MIG WELDED Al-Zn-Mg ALLOY

Abstract

The effect of pulse frequency at four different levels of mean current on the mechanical properties of the weldment of Al—Zn—Mg alloy (Zn 4.5•., Mg 1.25•., Mn 0.45 /, Fe 0.45•4, Si 0.3•., Cu 0.15•. and rest Aluminium) has been studied using the conventional End pulsed arc MIG welding process. A 1.6 mm 0 filler wire of composition A.1-4.5•. Mg (5183) have been used in this investigation for welding. The pulse frequency has been varied from 25 to 100 HZ. The welding of above mentioned alloy has also been carried out at •oF1 (convent Zonal MIG) and the weldment: properties have been compared with that produced by pulsed current process. Relatively better morphology of the weldmental has been marked in case of pulsed current process as compared to the conventional one. However, maximum refinement is found in weldmetal at some critical levels of frequency at all cases of mean current. A somewhat better morphology of the recrystallized zone in HAZ has been found in weldments produced by pulsed arc welding process in comparison to the conventional one. The porosity content of the weldmet al produced at different welding parameters has also been estimated and is found to be affected by pulse frequency variation. The bead shape has also been found to be significantly affected by pulse frequency variation, the weld bead geometry produced at higher pulse frequency have been found to be somewhat similar as in case conventional welding. The mechanical properties such as hardness, tensile strength and fatigue properties of weldment have been evaluated and found better in the welds made under current pulsation mode as compared to that of conventional one. It has been observed that the mechanical properties are being affected by micro-structure of the deposit, porosity content and the amount of residual stresses depending on thermal cooling cycle.