Physical Simulation of Laser Surface Treatment to Study Softening Effect on Age-Hardened Aluminium Alloys

Abstract

The automotive industry is interested in manufacturing components with tailored mechanical properties. To this end, advanced heating treatments can be exploited to obtain the so-called Tailored Heat-Treated Blanks (THTB). However, mechanical properties are strongly affected by the process parameters of heating treatments, which require a preliminary design. Physical simulation can be a decisive tool in this phase to obtain useful information at the laboratory scale, even when heat treatments such as those carried out with laser technologies impose high heating and cooling rates on the material. This work uses physical simulation to investigate the changes in strength and ductility caused by laser heat treatment (LHT) on aluminum alloys hardened by aging; the methodology was implemented on the EN AW 6082 T6 alloy. First, a finite-element (FE) transient thermal model was developed to simulate LHT by varying the process parameters (laser power/peak temperature and treatment speed). Second, the resulting thermal cycles were physically simulated by means of the Gleeble 3180 system. Third, the strength and the ductility of physically simulated specimens were evaluated through micro-hardness and tensile tests; to study aging effects, investigations were performed both (i) right after Gleeble tests (samples in the supersaturated solid state, i.e., as-physically simulated (APS) state) and (ii) after one week from Gleeble tests (aged specimens—T4 state). The obtained results show that there are peak temperatures that guarantee maximum softening levels for each investigated state (T4 and APS). The optimal peak temperature ranges are in agreement with the data in the literature, demonstrating that the proposed methodology is suitable for the study of softening phenomena on aging-hardened aluminum alloys.

Comparison of Flow Behaviors at High Temperature of Two Press Hardening Boron Steels with Different Hardenability

“…This system is able to reproduce high heating rates (up to 10 3 K/s) thanks to the Joule effect [23]. However, to reproduce rapid cooling rates, careful specimen design can be required if the water-cooled jaws surrounding specimen and the external cooling are not sufficient to achieve the required cooling rate [24,25]. Usually, the external cooling system is avoided due to oxidation problems caused by the absence of vacuum in the test chamber.…”

“…To find the specimen geometry that met these requirements, the 3D transient FE thermo-electric model, already described by Palmieri et al [24,25], was exploited.…”

“…A 3D FE model developed in COMSOL Multiphysics (version 5.6, Comsol Inc., Burlington, MA, USA) [24,25] was exploited to identify the specimen geometry that ensures during the thermo-mechanical tests low thermal gradient and a cooling rate able to characterize the material in the austenitic field. This model numerically simulates the thermo-mechanical tests in the Gleeble system, by coupling the thermal and the electrical physics.…”