Processing effects on hot tearing tendencies of die-cast magnesium components
(English)Manuscript (preprint) (Other academic)
A commercial AM50 Mg component was die cast with various process parameter settings. It was found that many of the process parameter settings investigated had a significant effect on the tendency for hot tears to form in critical sections of the component. A fast cavity filling helped to reduce the hot tearing tendency. This was explained by smaller temperature variations inside the casting immediately after cavity filling, which would cause less thermal stresses to form during solidification. Shorter mould opening time was also found to decrease the hot tearing tendency as a result of reduced tensile stresses inside the casting before mould opening. Severe hot tears formed when using an increased intensification pressure. In an attempt to explain this observation, numerical calculations were performed to investigate how the intensification pressure affects the solidification rate and the fraction solid gradients across the casting. It was found that a higher intensification pressure gives rise to steeper temperature gradients and fraction solid gradients during solidification between the surface and the centre of the casting. This would facilitate the initiation of hot tears but also flow of segregated liquid into the opening tears. It was also observed that hot tears in many cases have been filled, partially or even completely, by strongly segregated liquid, which in the Mg-Al system solidifies into a very brittle material.
Mg alloy, die casting, hot tearing, process parameters, numerical calculation
Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-85351OAI: oai:DiVA.org:liu-85351DiVA: diva2:570354