EVALUATION OF SOLDERING RESISTANCE OF CrAlN COATINGS INTENDED FOR APPLICATION ON HIGH PRESSURE DIE CASTING TOOLS

During high-pressure die casting (HPDC) of aluminum alloys the tool surfaces are exposed to extreme conditions as high temperatures, molten metal impact at high velocities, high pressure, corrosive environment, alternate heating and cooling cycles and abrasive wear. In such conditions tool surfaces suffer from thermal fatigue, erosion and soldering wear. As a result of tool wear, machine downtime and tool maintenance increases which cause significant financial losses. To reduce these losses and to extend the tool life, HPDC tool surfaces are submitted to plasma diffusion treatments and deposition of PVD (Physical Vapor Deposition) coatings. Therefore, in this study, the performance of duplex CrAlN coatings with three different chemical compositions was evaluated. The performance of the coatings was investigated in term of its soldering tendency to Al-Si-Cu alloy, using a detachment test. This test involves formation of a cylindrical casting on flat coated surfaces which is detached after the solidification and a required force is recorded. After detachment the analyses of contact surfaces reveal the soldering mechanisms and a sticking tendency of cast alloy toward investigated surfaces. For these purposes we employed 3D profilometry and different microscopy techniques. The cast alloy is kept in contact with the investigated coatings for four predetermined periods of time. The scanning electron microscopy (SEM), on all coatings, revealed the remnants of cast alloy (solder) after detachment tests and also a prominent coating delamination. The soldered area for different coatings has the same trend for different periods of contact with molten alloy. However, the amount of coatings delaminated area is different and closely correlates with samples detachment force. Higher detachment force is addressed to larger coating delamination area. It was found that the chemical composition of investigated coatings has modest influence on the soldering phenomena.