Investigating the effect of GTAW parameters on the porosity formation of C70600 copper-nickel alloy

Abstract

ABSTRACT In this study, the optimisation of welding parameters was investigated in a cupronickel alloy. The welding process was gas tungsten arc welding (GTAW) which is a prevalent method for welding pipes. The filler material type, shielding gas, and welding conditions were considered constant parameters, while heat input, shielding gas flow rate, wind flow speed and arc length were the variable parameters. In order to control variables precisely, the test coupons were assembled on a hand-made rotating machine with a controlled rotational speed. The microstructure and mechanical properties of the welded specimens were examined through the metallography and tensile test, respectively. The results showed that the optimum heat input and flow rate, which resulted in the lowest amount of porosity, were 10.2–11.3 kJ/cm and 6 L/min, respectively. It was also shown that by increasing the wind flow speed from 3 to 10 km/h, the porosity increased from 1.4% to 14.8%. In addition, reducing the arc length from 2 to 1 mm led to better weld protection and arc stability and consequently resulted in decreasing the amount of porosity from 1.1% to 0.23%. The tensile test results showed that the ultimate tensile strength of the welded specimen using appropriate parameters will be significantly reduced if improper welding parameters are used. The main reason for this decrease was the increase of porosity.