Abstract
For lightweight constructions, joining dissimilar metals is often indispensable to achieve exceptional properties. A common challenge is the bonding of steel and aluminum parts. The use of cold-sprayed coatings as a bonding agent is an innovative approach for high pressure die casting (HPDC) aluminum-steel hybrid components in order to achieve a metallurgical bonding, although it comes with high requirements in terms of coating adhesive and cohesive strength. Therefore, the main aim of this study is the optimization of a post-processing treatment of cold-sprayed coatings in order to improve the cohesive strength to help the introduced coatings withstand the mechanical and thermal stresses during HPDC. The effect of the heat treatment on the mechanical properties of the cold-sprayed Al99.0 and AA7075 coatings was investigated. Freestanding coatings were heat-treated at a temperature of T = 400 °C for different dwell times in order to analyze the recrystallization kinetics through hardness measurements. Two different heat treatment states along with an as-sprayed condition were chosen to investigate the evolution of the mechanical properties of the coatings by means of 3-point bending tests. Besides the softening of the coatings during the heat treatment, sintering effects at splat boundaries and their impact on fracture mechanisms were investigated using electron microscopy.
Highlights
The use of cold-sprayed coatings as a bonding agent is an innovative approach for high pressure die casting (HPDC) aluminum-steel hybrid components in order to achieve a metallurgical bonding, it comes with high requirements in terms of coating adhesive and cohesive strength
The application of coatings via cold gas spraying (CGS) for the high pressure die casting (HPDC) of aluminum-steel hybrid compounds has been analyzed in previous studies
A typical temperature of T = 400 °C was selected for soft annealing the AA7075 alloy
Summary
The application of coatings via cold gas spraying (CGS) for the high pressure die casting (HPDC) of aluminum-steel hybrid compounds has been analyzed in previous studies. It was shown that the deposition of AA7075 (AlZn5.5MgCu) and AA4145 (AlSi10Cu4) coatings on steel inserts can provide a better wetting by the aluminum melt during HPDC and, facilitate a solid metallurgical bonding between the aluminum and the steel parts (Ref 4-6). These coatings were prone to intersplat cracking either during casting due to the high kinetic energy of the aluminum melt, or afterward when loaded in shear tension. Heat treatment (HT) appears to be a promising solution to improve the ductility and to minimize the amount of intersplat cracking of the CGS coatings (Ref 79)
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