Increasing of the melt quality in Al-Si-Mg alloys by remelting

Increasing of the melt quality has been always a primary importance for production of high quality Al-Si-Mg castings. Therefore, a variety of methods have been developed for decreasing both the hydrogen and oxide content of these alloys. The present study aimed to introduce a noble method for increasing the quality of molten Al alloys which is based on the remelting of the alloy inside the crucible. We used reduced pressure test (RPT), high resolution three dimensional X-ray radiography, density measurement, metallography, image analysis and tensile test to determine the effects of remelting on the quality of the Al A356.2 melt. Results of density measurement showed that remelting increased the density of the alloy by 1.16 %( 31 Kg/m3).Results of 3D X-ray radiography and analysis of images form study of the microstructure revealed that remeltingof the alloy: a) Decreased the volume and area fraction of pores by about 39 and 49 %, respectively. b) Decreased the surface and volume number density of pores and bifilm index of the alloy by about 36, 33and 55%, respectively. The volume and area fraction of pores are directly related to the hydrogen content of the melt, while the surface and volume number density of pores and bifilm index are related to the amount of double oxide films in the alloy. Therefore, the results clearly indicated that remelting decreased both hydrogen and oxide film content of the alloy Furthermore, results of tensile test showed that remelting increased the tensile properties of the alloy remarkably. For example, twice remelting of the alloy increased the UTS and El% of the alloy by about 19 and 97%, respectively.

کلیدواژه ها:

Double Oxide films ، Degassing ، Al-Si-Mg Alloys ، Porosity ، Density