Formation and distribution of porosity in Al-Si welds

by Legait, Pierre-Alexandre.

Aluminum alloys are the subject of increasing interest (in the automotive industry, as well as aircraft industry), aiming to reduce the weight of components and also allowing a profit in term of energy saving. Concerning the assembly, riveting has been widely used in the aircraft industry, whereas welding seems to be promising in the car industry in the case of aluminum alloys. Nevertheless, welding can generate defects, such as porosity or hot cracking, which could limit its development. One of the major problems associated with the welding of aluminum alloys is the formation of gas porosity. Aluminum alloy cleanliness remaining one of the aluminum industry’s primary concerns, this project focuses on the formation and distribution of porosity in Al-Si welds. A literature review has been performed, to identify the mechanisms of porosity formation in welds and castings. Porosity distribution in welds has been investigated, based on three different welding techniques: hybrid Laser/MIG welding process, the electron beam welding process, and the MIG dual wire welding process. Porosity distribution results provide information on to the porosity formation mechanisms involved during welding. A complete microstructure, microhardness and EDX analysis have been carried out, to describe and quantify the solidification process within the welds. i