Investigation On Hot Tearing Behaviors Of Mg-(Zn)-Ca Magnesium Alloys

In recent years, due to continuously explore and seek knowledge of science andtechnology researchers, the range of applications of magnesium alloy material are morewidely. However, magnesium alloys have a wide range of solidification temperature andlarge amount of solidification shrinkage, show a high susceptibility to hot tearing duringthe solidification process. Recently, magnesium alloy parts not only have thin wall but alsohave complex structure, higher hot tearing susceptibility will limit its application. Soinvestigations on hot tearing behaviors of magnesium alloys have a very importanttheoretical significance and engineering application value.Currently, most of previous experiments about the behavior of hot tearing werecarried out limited on Mg-Al series magnesium alloy, but seldom concerned about otherseries. During alloy design the alloy composition which have higher hot tearingsusceptibility will be able to avoid if the hot tearing susceptibility of magnesium alloys areinvestigated clearly. This paper uses a self-designed hot tearing data acquisition system,This system can collect data of time, temperature and contraction force in the same time, inaddition, this paper using liquid paraffin osmosis method and vacuum equipment toquantitative measure hot crack volume. This experiment set Mg-Ca series and Mg-Zn-Caseries alloys as the research object and investigations on hot tearing susceptibility ofMg-（Zn）-Ca alloys for different Ca content.The results show that, for Mg-Ca series binary alloys and Mg-Zn-Ca series ternary alloys,the grains of alloy refine, hot crack volume decreases gradually, the feeding effect of alloysincreases and the hot tearing susceptibility gradually decreases with Ca content increasing.the feeding material in the crack of the two series alloys are the mixture of α-Mg、Mg₂Caphase and the mixture of α-Mg、Ca₂Mg₆Zn₃phase、Mg₂Ca phase. When the Ca content isless, liquid film of hot tearing is thin. As the Ca content increases, the liquid film in thecrack location constantly thickening and the folds increasingly obvious, so reduce the hottearing susceptibility of the alloy. For the same alloy composition, solidification contraction force on the edge is stronger than that in the inner in the solidification process.In addition, the higher of Ca content, the relaxation amplitude of force when crackinitiation. For the same decreases range, the remaining liquid phase is higher for the higherCa content alloys, the separation of dendrites can be feed better. For Mg-Ca series binaryalloys and Mg-Zn-Ca series ternary alloys, the increased solidification contraction forcerecorded from start solidification to300oC is inversely proportional to the crack volume. Itmeans that, hot crack volume is larger, the released force is larger, the solidificationcontraction force measured is smaller.