Study on the Filtering Purification of AZ91 Magnesium Alloy

Abstract

High quality magnesium casting depends significantly on the purification of its alloy melt. However, it is very difficult to obtain high-quality magnesium alloy melt due to its high reactivity and its tendency of combustion. The fluxing processing, a traditional purification method for magnesium melt, not only bears the risk of flux inclusions but also is facing more and more environmental pressure today. Therefore, the effective substitutes for fluxing processing, such as physical filtering method, are paid more attention recently. In this paper, the effects of technological conditions including the pore size of stainless steel mesh and the filtering temperature on the purification degree of AZ91 alloy melt were investigated in the mesh filtering processing, in which 2 wt.% calcium was added into the melt in order to obtaining ignition-proof property. The results indicated that mesh filtering processing could improve the purification degree markedly, and the purification degree increased with the increase of filtering temperature properly or the decreased of pore size of mesh. However, too high filtering temperature would lead to the increasing of the tendency of oxidation and combustion, and too small pore size would decrease the filtering ability of mesh which would lead to the interrupting of purification operation.

Inclusion removal and grain refinement of magnesium alloy castings

“…Stainless steel meshes are typically used for the filtration of Mg melts due to their relatively low cost, high availability and non-reactivity with Mg melts. Le et al [79] used stainless steel filters of decreased pore size in AZ91 + 2 wt.% Ca alloy. They found that the finest mesh caused a reduction in the number and maximum size of the inclusions.…”

“…They found that the finest mesh caused a reduction in the number and maximum size of the inclusions. Also, they determined that low pouring temperatures (~700°C) reduced the oxidation potential of the melt and the inclusion levels [79]. Tardif et al [80] also examined the use of knitted steel mesh filters to remove melt inclusions in permanent moulds.…”

Inclusions in magnesium and its alloys: a review

“…Stainless steel meshes are typically used for the filtration of Mg melts due to their relatively low cost, high availability and non-reactivity with Mg melts. Le et al 106 used stainless steel filters of decreased pore size in AZ91+2 wt-%Ca alloy. They found that the finest mesh caused a reduction in the number and maximum size of the inclusions.…”

“…Also, they determined that low pouring temperatures (∼700°C) reduced the oxidation potential of the melt and the inclusion levels. 106 Tardif et al 107 also examined the use of knitted steel mesh filters to remove melt inclusions in permanent moulds. Two and four ply filter configurations were examined and were found to entrap mainly MgO and some Al–Mn–Fe intermetallic particles.…”