Effect of the laser surface treatment on structure and mechanical properties of AlZn10Si8Mg cast alloy

Abstract

The laser surface melting/hardening is method which provides increasing mechanical properties of secondary (recycled) Al-Si cast alloys for automotive industry. Improvement of mechanical properties and structure of secondary aluminium alloys can often significantly increase the lifetime of casting and reduce costs for fuel and reduction of environmental loading. Self-hardening Al-alloys (Al-Zn-Si-Mg alloys) introduce an innovative class of light Al-alloys. AlZn10Si8Mg alloy is used for engine and vehicle constructions, hydraulic unit and mould making without the need of heat treatment because this alloy is self-hardened. For this study, a laser beam of Nd: YAG laser, BLS 720, with laser power 50 and 80 W, was used. The final microstructure of Al- alloys depend on the laser process parameters. The laser beam action on the surface of the experimental alloy has changed the microstructure of the material. Melting area is alpha-phase with much fine columnar dendrites morphology without the presence of Si-particles and intermetallic phases. In the transition area, grain refinement of eutectic Si (finer and rounder Si particles) as the modify action of the laser was observed. By increasing the laser power the microhardness of surface layers decreases. In the surface layer (after the 80 W laser beam action), cracks due to uneven heat transfer of the material were observed.