Chemical pretreatment and adhesive bonding properties of high-pressure die cast aluminum alloy: AlSi10MnMg

High-pressure die cast (HPDC) aluminum components are increasingly integrated into the assembly of vehicles for weight-reduction. Adhesive bonding of HPDC aluminum alloys with other structural parts has been ever challenging in the hybrid construction of automobiles due to the inherent contamination of casting surfaces by die lubricants. In this study, the residual lubricant on HPDC AlSi10MnMg plates was quantitatively measured using surface sensitive techniques. Chemical pretreatment processes were designed and the effectiveness of pretreatment processes was evaluated by comparison of surface morphologies and chemical compositions, as well as adhesion properties before and after aging. It is found that the initial single lap-shear strength of the as-cast AlSi10MnMg plates shows a location-dependence and is influenced by casting parameters, particularly in the regions away from the melt-ingate of the die, where a high amount of residual lubricants is often measured. Chemical pretreatments including degreasing, deoxidation and deposition of titanium-oxide conversion coatings can improve the surface homogeneity through removal of residual lubricants from and replacement of oxide layers at the surface of HPDC AlSi10MnMg alloys. The chemical treatment process consisting of degreasing in alkaline solutions, deoxidation in fluoride-containing sulfuric acid solutions and dipping in hexafluorotitanic acid solutions has been identified to be the most effective pretreatment procedure by generating a rough surface in a micro-scale, and removing residual lubricants to a large extent from as well as inhibiting corrosion at the surface of HPDC AlSi10MnMg plates. The effectiveness of this pretreatment process was also confirmed by durability assessment of epoxy-bonded single lap-shear joints and wedge specimens after environment exposure to 70 °C, 100% R. H. for 4 weeks.