Analysis of the Influence of Surface Finishing on the Performances of Dies for HPDC

The Al-alloy die casting die is a sector where the operating environment imposes a very severe aggression to hot working tools. Steel grades for such application, techniques for their surface modification and specifically conceived lubricants are continuously improved so as to limit Al soldering. Within this scenario the interaction between lubricant and die surface and the effect of finishing levels of such surface is poorly studied. This paper deals with a study of the influence of dies surface roughness on the working behavior of a die casting lubricant and on surface damages of a tool steel grade. Tool steel samples were prepared for the research and two different levels of surface roughness (as polished and as finely sand blasted) were investigated. Apart from the base characterization of steels and surface, two specific test rigs were used to study the lubricant-tool steel surface-Al alloy interactions. One of test rig was devoted to study the coupling principles of tool die surface-lubricant, while the other test rig was used to perform a cyclic immersion test in molten Al-alloy. The derived data were compared to the experimental investigation of cracks and craters as provided by cycling with a correlation with the surface finishing level of samples.