Performance of Ti/Zr and silane coating pretreatments on adhesive bonding of an automotive aluminium alloy produced using the Hot Form Quench (HFQ®) process

Surface pretreatments of an automotive aluminium alloy delivered in F temper and subsequently processed using Hot Form Quench (HFQ®), a novel press forming technique combining solution heat treatment, press forming and in-die quenching to produce high-strength aluminium alloys, for adhesive bonding have been explored. The performance of two commercial pretreatments including Ti/Zr and silane coatings, with either acid spray or alkaline immersion cleaning, was investigated. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM) were employed to characterize the surface chemistry and topography of the alloy after pretreatments. Adhesively bonded aluminium-aluminium single lap shear joints and double cantilever beam specimens were tested to evaluate the performance of the pretreatments on the bonding strength and fracture resistance, respectively. The FTIR and TEM techniques show that the natural oxides and near-surface deformed layer have been successfully removed, but the surface cleanliness level was sensitive to the cleaning approach adopted. New Ti/Zr oxide layers or silane films have been built upon the aluminium surfaces, which confirms that sound surface conditions for adhesive bonding can be obtained for parts produced using HFQ® from F temper input material.