Metal Additive Manufacturing Conference 2019

With additive manufacturing the internal cooling channels can be manufactured to an optimized geometry in order to have conformal cooling. In die casting soldering and heat checking are the main problems. Soldering is a result of the interaction between the steel and the molten aluminium. Heat checking is related to thermal fatigue. The development of AM powder is still at an early stage and the most AM grades on the market are easy to process with laser powder bed fusion, but not designed for the application. Therefore, thermal fatigue resistance has to be tested for existing and new materials. In the present investigation the influence of heat treatment and microstructure on soldering and thermal fatigue resistance was evaluated. Soldering testing was done where tool steel rods were submerged into molten die casting aluminium at 680 °C. The composition and thickness of the intermetallic layer of the samples were evaluated. To simulate thermal fatigue heating with induction was performed between 200 °C and 700 °C for 20000 cycles. Heating time was approximately 0.5 s, and total cycle 2.1 s. The materials were evaluated by measuring the crack depth in the heat affected zone in microscope. Maximum crack depth, mean value of the 10 deepest cracks, and crack density were calculated. Microstructure characterisation was done in SEM.The result showed that the heat treatment influenced microstructure, mechanical properties, crack depth and crack density. Soldering resistance was more sensitive to chemical composition of the steel. Based on these observations the materials were ranked in order to predict the performance of the tested steels in die casting application. Influence of heat treatment on microstructure and properties was discussed to develop new heat treatment regimes.