Research On Microstructure And Properties Of High-strength Flameretardant Mg-17Al-8Ca-xMn Alloy

In this paper,the morphology and type of primary phase of Mg-17Al-8Ca alloy with high alloy content are controlled by homogenization heat treatment,high temperature extrusion deformation,and the addition of trace Mn elements.The homogenization heat treatment and high temperature extrusion deformation have been improved.The mechanical properties of the high alloy content Mg-17Al-8Ca alloy can produce a high alloy content Mg-17Al-8Ca alloy with low cost,excellent performance and good flame retardant effect.The effect of homogenization heat treatment process,extrusion temperature and Mn element content on the type,quantity and size of the second phase in the alloy,and the effect of Al content on the flame retardancy of high alloy content MgAl-Ca alloys were studied.The strong plasticity and flame-retardant mechanism of MgAl-Ca alloy with high alloy content are obtained.The two-stage homogenization heat treatment process of 420? low temperature homogenization heat treatment for 12 hours and 500? high temperature homogenization heat treatment for 12 hours has realized the full re-dissolution of the low melting point Mg17Al12 phase in the Mg-Al-Ca alloy and promoted the transformation of the C36 phase into At the same time,the morphology of the C15 phase and the primary phase changed from lamellar to granular.Extrusion deformation can also promote the transformation of C36 phase into C15 phase,and high temperature extrusion deformation at 450°C and 480°C can cause a large amount of C15 phase to precipitate in the alloy,and the size of the particulate second phase can be refined to about 2?m.It is completely recrystallized,and the recrystallized grain size is about 2 ?m.The tensile strength of Mg-17Al-8Ca alloy is 362 MPa,the yield strength is 262 MPa,the elongation is 5.6%,and the elastic modulus is about 51 GPa.Adding a certain amount of Mn element can promote the second phase in the as-cast alloy to tend to be elongated,promote the precipitation of the elongated C15 phase during the homogenization heat treatment,and the transformation of part of the particulate second phase from the C36 phase to the C15 phase.At the same time,a small amount of Mn can also refine the second phase,recrystallize the grain size,and increase the recrystallization ratio.The tensile strength of the 400? extruded Mg-17Al-8Ca alloy with0.4wt.% Mn can reach 361 MPa,the yield strength is 241 MPa,and the elongation is about7.4%.Adding a small amount of Mn can not only reduce the extrusion temperature but also increase the elongation.The alloys used in this article can be smelted and cast without protective gas.The ignition point of AXM17802 alloy can reach up to about 1250°C.The oxide film of the alloy is composed of a large amount of heat-resistant Mg Al2O4 spinel and a small amount of Al2O3.With the increase of Al content,the ignition temperature gradually increases,the quality of the oxide film gradually improves,and the flame retardant performance of the alloy gradually improves.