TWI Industrial Member Report Summary 555/1996
R J Wise
Polymer-coated material joints in aluminium alloy have shown high levels of resistance to moisture and tested specimens exhibited cohesive failure almost exclusively.
In 1991, TWI began work on a new technique for joining dissimilar materials called the polymer-coated material (PCM) joining technique. (1) This technique, originally developed for joining thermoplastics to metals, involves coating non-thermoplastic components with a layer of thermoplastic from solution. Coatings applied in this way tend to adhere well to the substrate (provided that the chemistry is suitable) due to good wetting.
To complete the joint, the coated components are welded to thermoplastic components using a thermoplastics welding technique, such as resistive implant or induction welding. In order to improve the mechanical properties of the joints, a surface pretreatment may be applied to the non-thermoplastic components prior to coating. In the case of aluminium alloy, this is typically unsealed anodising, which serves to enhance the mechanical keying and chemical bonding of the coating.
In previous work, (1) joints between aluminium alloy and the PEEK/carbon fibre thermoplastic composite APC2, were manufactured using resistive implant welding with single lap shear strengths of up to 30MPa (4300psi).
The PCM joining technique offers a speedy route for joining dissimilar materials where the final joining operation can be rapid (<60sec) because it is a weld. PCM joints can also be dismantled on the application of sufficient heat to remelt the thermoplastic coating.
- To assess the resistance of PCM joints to high humidity.
- To ascertain the locus of failure in joints so that weaknesses in the technology could be isolated and subsequently eliminated.