Improvement of adhesive bonding in aluminium alloys using a laser surface texturing process

A study has been made of the surface modification of aluminium alloys using the Nd-YAG pulsed solid-state laser technique. The melt cavities on an aluminium alloy surface produced by the laser have two main features, namely non-periodic concentric rings and microcracks. The concentric ring structures effectively increase the surface area, enhancing the adhesive bond quality, whilst the microcracks propagated into the sub-surface level are detrimental to the long-term mechanical performance of the metal substrate. The laser pulse shaping technique was introduced to control the appearance of these features, whereby the original rectangular laser pulse shape could be altered, so that a different laser intensity and cooling rate could be used. The laser intensity is found to be a predominant factor for the formation of the concentric ring structures. In the high intensity range the laser beam excited oscillations, generating circular waves which are reflected by the frozen melt pools. The cracking phenomenon seems mainly material dependent, but is less sensitive to the intensity of the laser beam.