Study Of The Creep Properties And Hot Compression Deformation Behavior Of AM80 Alloy Containing Ca And Micro Sr

The lightweight material has maintained a sustainable and rapid development as the requiremet of reducing fuel consumption and mitigating environmental pollution around the world. But the creep vesistance of comercial magnesium alloys used is still inferior, or the cost is too high to use in the automotive industry. At present, the vast majority of magnesium products for the automotive applications are in the form of die castings. Wrought magnesium alloys have so far found very limited usage, although they are expected to have higher strength and ductility than the cast counterparts. One of the barriers to the applications of wrought magnesium alloys is their low workability, as a result of hexagonal crystal structure. Therefore, it is necessary to explore the hot working potential of this kind of materials. The present study aims to investigate the effects of alkaline elements Ca and Sr additions on microstructure, creep properties and the flow stress behavior and microstructure evolution of AM80 magnesium alloy.In the present paper, the effects of alkaline elements Ca and Sr additions on microstructure and mechanical properties of AM80 magnesium alloy had been investigated, by using Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and creep properties testing at elevated temperature. And hot compression tests of AM80-0.2Sr-1.5Ca magnesium alloy was performed on Gleeble 1500 at strain rates between 0.01～10s-1 and deformation temperatures between 300～450℃, respectively. The influence of the parameters on the stress-strain curves was analyzed to determine the constants in the constitutive equations. The microstructures of magnesium alloy during compression were observed by using MM-6 horizontal optical microscope (OM) of LeitZ CoMPany Limited of West German and Scanning Electron Microscopy (SEM) of JEOL JSM-5610LV.The results showed that microstructures of the as-cast alloys were refined by adding 0.2% Sr and Ca which the content is between 0.5% and 2.5%. A high-melting point Al2Ca phase dispersedly distributed at the grain boundaries in the AM80 alloy due to the priority combination of Ca and Al. And the formation ofβ-Mg17Al12 phase was reduced. The mechanical properties of the alloys were also improved due to the existence of the addition of Ca and Sr. The non-continuousβ-Mg17Al12 phase precipitated at the grain boundaries and perpendicularited to the grain boundaries, decreasing the creep properties of AM80 magnesium alloy. The elevated temperature creep property of the alloys are greatly improved because of low-melting point P-Mg17Al12 phase being replaced by high-melting point Al2Ca phase which preventing the grain boundaries sliding. The creep mechanism was most best when the mass fraction of Ca is 2.5%. The relation between stress and strain of AM80-0.2Sr-1.5Ca alloy is obviously influenced by strain rate and deformation temperature. The flow stress increases with the increase of strain rate, and decreases with the increase of deformation temperature. Furthermore, the optical microstructures observation shows that the dynamic recrystallization is main mechanism for grain refinement and flow softening under the test conditions. This mechanism is influenced by deformation parameters. The recrystallized grain size increases with the increasing of deformation temperature and decreases with the increasing of strain rate.