Effect of Welding Speed on the Microstructure and Corrosion Properties of Weld and Heat Affected Zones in GTA Welded AA2014 Alloy

The microstructure and corrosion properties of weld fusion zone and the heat affected zones of gas tungsten arc (GTA) welded AA2014 alloy, welded at varying speeds of 1.5mm/s, 2.5 mm/s and 3.5 mm/s were examined for gaining knowledge on the effect of welding speed on corrosion behavior at localized regions of the weldment. The macrostructure and microstructure of the welds were evaluated with optical microscope. The corrosion properties were examined with potentiodynamic polarization in aqueous 3.5% NaCl solution. The GTA welding has resulted in grain refinement fusion zone and dispersion of coarse Al2Cu phases within the grains and along the grain boundaries of heat affected zones. With increase in welding speed the grain size of AA2014 at the fusion zone reduces significantly and also the corrosion resistance of the fusion zone and heat affected zone could decrease as it shows higher negative corrosion potential.

Correlating Tensile Properties with Microstructures of Various Regions in Gas Tungsten Arc Welded AA2014 Alloy

AA2014 is a heat treatable aluminium alloy found its application in light weight structures owing to its superior strength to weight ratio. The alloy was welded with automatic gas tungsten arc welding. The microstructure and mechanical properties of each zone such as parent metal (PM), heat affected zone (HAZ) and fusion zone (FZ) of the weldment were studied using optical microscopy, microhardness survey and micro-tensile testing. The PM with elongated grains with evenly distributed Al2Cu phases showed a tensile strength of 456 MPa and 24% elongation; the HAZ and FZ offered a reduction in strength and ductility. The grain coarsening with segregation of continuous string of Al2Cu along grain boundaries in HAZ and the formation of coarse dendritic grains with continuous network of brittle Al2Cu and a minor fraction of porosity at interdendrite in FZ were attribured to the observed strength reduction in these regions. Keywords: AA2014 alloy; gas tungsten arc welding; optical microscopy; microhardness; micro-tensile testing.