PLA deposition on surface treated magnesium alloy: Adhesion, toughness and corrosion behaviour

Abstract

This study shows that the use of polylactic acid polymer (PLA) coatings deposited by dip-coating on AZ31 magnesium alloy can increase the integrity of the system and the fracture toughness of magnesium substrates treated by plasma electrolytic oxidation (PEO). This provides a novel and promising use of a multilayered system made of fully biocompatible materials. The maximum adhesion strength value for PLA coatings on AZ31 was >50% higher than the maximum one for AZ31/PEO/PLA, while the maximum bending strain tripled. The limitations observed in the AZ31/PEO system arise from the brittle nature of the oxides formed during PEO treatments; their negative impact is reduced when incorporating a PLA layer that is capable of filling the pores and sealing the cracks of the PEO layer. PLA coatings reduce corrosion of AZ31 and maintain the corrosion protection provided by the PEO treatments. The characteristics of the PLA coatings on AZ31 Mg alloy and on AZ31/PEO systems were evaluated by using a Taguchi design of experiment (DOE) method using the following processing parameters: (i) number of layers, (ii) withdrawal speed and (iii) polymer concentration. The effect of these three degrees of freedom and, the surface treatment has been evaluated with regards to different properties desired for the coatings, i.e., adhesion, thickness, roughness, and corrosion resistance.