Aurélie Niel

Modelling hot cracking in 6061 aluminium alloy weld metal with microstructure based criterion

Abstract Hot cracking in welding is a complex phenomenon due to coupling between process, metallurgy and mechanical loading. A methodology based on process simulation, simple microstructural prediction and a pressure model along columnar grains is developed in order to integrate all factors that influence hot cracking. The model is based on some developments of Rappaz, Drezet and Gremaud and takes into account the influences of grain morphology, mechanical and welding thermal loading, on hot cracking. The model based on the microstructure behaviour is able to predict crack onset location in columnar grains on 6061 aluminium alloy.

Hot tearing test for TIG welding of aluminum alloys: application of a stress parallel to the fusion line

Defects control such as solidification cracking in aluminum alloys welding is an important industrial issue and must be carefully examined. This 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 hot cracking sensitivity and mechanical or 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 initial stress is applied on the test specimen parallel to the welding direction. During the test, a fusion line is made using Gas Tungsten Arc Welding (GTAW) 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 structure, which is characterized by the shape, size and the growth direction, and which depends on welding current and speed, plays a crucial role in the crack initiation. Microstructural features are observed using high speed camera recording and post mortem micrographs. Mechanical factors are varied by adjusting the welding parameters. The relationship between welding parameters, grain morphology, and sensitivity to hot cracking are 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 model.