Laser weldability and ageing characteristics of welds: laser weldability of commercially available A7N01 alloy (1)

Abstract

CO₂ laser or YAG laser welding of A7N01 alloy was carried out with the objectives of assessing its laser weldability, especially penetration and formation tendencies of cracking and porosity, and elucidating the causes of the reduction in mechanical properties of laser welds. The effect of plate thickness on weld penetration was recognized. Penetration of heat-conduction type welds was deeper at the relatively longer defocused distances in YAG laser welding. Cracking was formed more easily at a higher welding speed in a thicker plate. Porosity was formed in a keyhole type of partial penetration weld beads produced at low welding speeds of less than 100 mm/s. It was confirmed that the hardness of the heat-affected zone made in laser welding with a smaller heat input at a higher speed recovered appreciably at room temperature. The causes of the reduction in the hardness in laser weld fusion zone were attributed to the evaporation and the microsegregation of main strengthening alloying elements, Zn and Mg, during welding and subsequent solidification, respectively.

Keywords:

• laser welding
• aluminium alloy
• hardness
• tensile strength
• cracking
• ageing
• evaporation
• microsegregation

Acknowledgements

This study was part of a research project of the Laser Welding Committee of the Japan Light Metal Welding and Construction Association and we would like to express our gratitude to Prof. Matsunawa and Prof. Takemoto. The laser equipment was kindly supplied by Mr Inoue of the Applied Laser Engineering Center and Mr Kondo of the Advanced Materials Processing Institute, Kinki, to whom we give our thanks.