Experimental Investigation of Localised Laser Heat Treatment Effects on 6XXX Aluminium Alloys: Critical Insights into Numerical Modelling

To meet global emission reduction targets, high specific strength materials, such as 6XXX-series aluminium alloys, are integrated into automotive structures. Although self-piercing riveting (SPR) is a highly adopted joining technique in the referred industry, the low cold formability of these alloys can lead to failure in the sheet material. Thus, a promising solution is the application of a localised laser heat treatment that will promote the local softening of the material and, therefore, prevent its failure. A prior numerical study introduced localised laser heat treatment to solve the bottom sheet failure problem but simplified it by assuming homogeneous hardness throughout the treated thickness and strict confinement of the softened zone. However, these simplifying assumptions lack rigorous experimental validation. To address this gap, this work aims to assess the validity of these simplifications. For this purpose, an experimental analysis was conducted on four samples of AA6063-T6 subjected to a localised laser heat treatment applied to an annular region defined by internal and external diameters of 4 and 7.5 mm. The resulting hardness profiles were subsequently analysed. Results demonstrate that the laser-induced softening was not confined to the intended annular region and did not occur uniformly through the sheet thickness. These findings reveal discrepancies between the real softening behaviour and the assumptions adopted in the numerical model.