Influence of heat input and shielding gas flow-rate on the microstructure and mechanical properties of dissimilar welded AA1100 and AA6070

Abstract

This study examined the influence of heat input and shielding gas flow-rate on the microstructure and mechanical properties of V-joint welded aluminium alloys of 1100 and 6070 plates. The as-received AA6070 was an off-cut billet and was cast into a flat plate of 5 mm using the green sand moulding technique. AA1100 was used in the as-received condition. Plates of dimension 50 x 50 x 5 mm were prepared for the Tungsten Inert Gas (TIG) welding with heat input ranged between 52.5 J/mm and 69.1 J/mm and shielding gas (argon) flow rate of 7 and 13 L/min. The visual inspection indicated that welds were free common defects with no distortion. The results obtained from the experiments showed that the predominant phases in the microstructure of the samples were α − Al, AlSiO2 and AlFeSiO2, which characterised the strengthening mechanism of the weld joints. At a currentof 70A, and shielding gas flow rate of 7L min,the microstructure showed more of dendritic structure, which mainly contained α − Al and AlSiO2. When the gas flow rate increased to 10 L/min, the dendritic structure broke into platelets with no oxygen gas diffusion. The weld joint demonstrated the highest hardness value of 72 HV at 70 A and 13 L/min gas flow rate. The weld joint demonstrated the highest ultimate tensile strength of 86 MPa at 130 A and 10 L/min.