Model characterization and failure analysis of welded aluminium components including process history

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Abstract
There is currently a high level of interest in automotive and other industries to use aluminium extrusions for lightweight structural members. The preferred joining technology is robot controlled MIG welding to provide a fast, consistent, high-quality weld. The disadvantage, however, is that the high temperature fusion process causes metallurgical transformations adjacent to the weldline in the Heat Affected Zones (HAZ), which significantly reduce mechanical properties and provide lines of weakness. Under crash loading these zones are of special concern and techniques are needed to evaluate their performance. This paper investigates reduced mechanical properties in the HAZ of welded aluminium joints and proposes a failure law suitable for practical crash simulation of automotive structures. The work has necessitated a pragmatic approach in which a compromise is sought between the true representation of the void growth and fracture mechanisms that occur on a micro-scale and the need for a simplified macro-model appropriate for large scale CPU intensive structures. Simulation tools and techniques are also presented that enable the process history of the weld manufacture to be analyzed and results of the HAZ and modified mechanical properties to be mapped to the structural model for crash or failure analysis, thus limiting the need for extensive mechanical testing. Validation studies are presented on notched butt joints and dynamically loaded sectional welded joints.

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