Effect of shielding gas composition on low temperature toughness of Al5083–O gas metal arc welds

Abstract

There is an ever increasing range of shielding gases, which vary from the pure gases to complex mixtures based on argon, helium, oxygen, and carbon dioxide. The commercially available gas mixtures should be considered in terms of their suitability for ensuring arc and metal transfer stability, performance, and weld quality. The objective of the present paper is to study the toughness of Al5083–O aluminium alloy, to evaluate the variation of welding zone toughness as a function of the shielding gas composition and the testing temperature. To achieve these objectives, gas metal arc welding was performed with four different shielding gas compositions (100%Ar−0%He, 67%Ar+33%He, 50%Ar−50%He, and 33%Ar+67%He), and tests were carried out at four different temperatures, namely,+25°C (+77°F), −30°C (−22°F), −85°C (−121°F), and −196°C (−321°F). The welding zone was divided into four subzones for analysis, namely, weld metal, fusion line, heat affected zone, and base metal according to the notch position. Tensile and yield strengths did not show a great effect of testing temperature at +25°C to −85°C, but increased greatly at −196°C. Also, strain tended to increase as test temperature decreased. Shielding gas composition does not have a great influence on mechanical properties. The size and number of defects were least in the 33%Ar−67%He mixture. This shows that the higher the helium gas content, the lower the number of defects detected via radiographic inspection. In the impact test, the maximum load was lowest in the weld metal and highest in the base metal at room temperature, and the maximum load and displacement were higher and lower respectively at −196°C than those at other test temperatures, showing that the lower the test temperature, the higher the maximum load, without any special features related to the phase composition being observed in the load–deflection response. The absorbed energy of the weld metal notched specimens did not depend significantly on test temperature and shielding gas mixture. Conversely, the other specimens showed that as temperature was decreased, absorption energy increased slightly up to a maximum at −85°C, but then decreased markedly at −196°C.