EFFECT OF PULSE PARAMETERS ON THE CORROSION RESISTANCE, TENSILE STRENGTH & HARDNESS PROPERTIES OF THE MIG WELDED ALUMINUM ALLOY

Abstract

AI-Zn-Mg base alloy is known for their combination of good strength, corrosion resistance and weldability. Al-Zn-Mg alloys are used in aircraft industries, shipbuilding and other structures such as pressure'vessels, containers, tankers etc. AI-Zn-Mg alloy weldments were prepared using 6 mm thick extruded plates (7039) and 1.6 mm diameter Al+ 4.7% Mg filler wire at mean current level of 100 amp and 150 amp using pulsed MIG welding process. During welding, the pulse frequency was varied from 25 to 100 Hz. The effects of mean current and pulse frequency on weldment's mechanical such as hardness tensile strength and weldment corrosion properties in static and accelerated condition have been studied. The microstructure of Al alloys has a large influence on the corrosion as well as mechanical behavior. In particular the inter-metallic particles play an important role to determine corrosion and mechanical properties. The shape, size and chemical composition of inter-metallic particles are determined by;: the type of welding process and process parameters. Variations in microstructure and precipitates are caused by non-uniform heat input and cooling rate along welding zone and HAZ. We find relatively fine structure of weld metal made by pulsed GMAW process as compared to conventional one. However the extent of refinement was found to vary with the variation in pulse parameters. Hardness, tensile strength and corrosion resistance properties of weldments were. found better in welds prepared with pulse current as compared to conventional one. At a given current the hardness and tensile strength of the weld deposit found to be increased with the increase in pulse frequency. Corrosion resistance of GMAW welded AI-Zn-Mg alloys is more for higher frequency ranges at. given current. But it is observed that with increase in current the corrosion resistance has decreased both for static and accelerated corrosion condition in 3.5% NaCl solution. It is also observed that at initial stage for 40 days corrosion rate is high but later on it was found decreased under static condition.