Hot tearing test for TIG welding of aluminium alloys: application of a tensile load parallel to the fusion line

International audienceDefects control such as hot cracking in aluminum alloys welding is an important industrial issue. Understanding of hot cracking phenomenon is a complex problem involving process, material and mechanical loading due to clamping. Several tests have been previously developed in order to characterize the material propensity to hot cracking. The purpose of the present work is to study, using a new hot cracking test and numerical simulation, the relationship between mechanical and metallurgical factors in order to better identify the parameters leading to hot tearing during welding. The originality of the test presented here is that an external stress is applied on the test specimen parallel to the welding direction. The advantage of this test, compared to others like Varestraint test, is its simplicity which is interesting for an industrial use. A fusion line is made with a Tungsten Inert Gas (TIG) arc welding process on a thin sheet of aluminum alloy (6061). The crack initiation occurs once steady state thermal conditions are reached. The present test enables to distinguish between the structural effects on a global scale and the microstructural effects on a local scale. Microstructure control is made possible by adjusting welding power, welding speed and sample geometries. The grain morphology plays a crucial role in the crack initiation. It depends on the intensity and the welding speed and the specimen geometry. It is characterized by the shape, size but also the direction of grain growth that influence the cracks initiation. Microstructural features are observed using high speed camera recording and post mortem micrographs. Mechanical factors are varied by adjusting the welding parameters and the applied prestress. The relationship between welding parameters, morphology of the generated grain structure, and sensitivity to hot cracking were discussed. Experimental measurements and numerical results will help to better determine global and local conditions at the onset of hot tearing and to compare those conditions using existing hot tearing criteria