Study on porosity formation in laser welds in aluminium alloys (Report 1): Effects of hydrogen and alloying elements

Abstract

Summary The CO2 laser welding of aluminium alloys, A3003, A6061, A6N01, A5052, A5083 and A5182, was carried out at different welding speeds and the behaviour of porosity formed in the laser welds was investigated to make clear the mechanism of porosity formation. Three types of porosity were observed. The observed number of voids (Type A) of less than 50μm diameter decreased with an increase in welding speed and solidification rate because of lack of time for nucleation and growth of gas bubbles during laser welding. According to the analysis of porosity gas in the laser welds of A3003, A6061, A6N01 and A5052, hydrogen was about 90 vol% of total porosity gases and the rest was nitrogen. And for A5083 and A5182 alloy welds with deeper penetration, a small amount of helium, used as a shielding gas, was also detected. Besides, for the laser welds in Al-Mg alloys, the majority of porosity was formed along the solute band with Mg enrichment. The Mg induced polygonal porosity (Type C) and larger porosity (Type B) was observed in the upper part of welds. The Mg concentration on inner surfaces of voids was found to be about 18 mass% by means of EDX analysis of alloying elements. It is concluded that porosity formation is greatly influenced by solidification rate, i.e. welding speed and alloying elements.