Lost foam casting(LFC)technology has been widely applied to cast iron and cast steel.However,the development of LFC for Al and Mg alloys was relatively slower than that for cast iron and cast steel.The application of LFC to Al and Mg alloys needs more effort,especially in China.In this paper,the development history of LFC is reviewed,and the application situations of LFC to Al and Mg alloys are mainly discussed.Meanwhile,the key problems of LFC for Al and Mg alloys are also pointed out.Finally,the prospects for LFC technology are discussed,and some special new LFC technologies are introduced for casting Al and Mg alloys.In future,the development trends of green LFC technology mainly focus on the special new LFC methods,metal material,coating,heat treatment,new foam materials as well as purification technology of tail gas,etc.
The microstructure evolution and mechanical properties of Mg-15Gd-3Y alloy were investigated in the as-cast and heat treated conditions.The microstructure evolution from as-cast to cast-T4 states involved α-Mg solid solution+Mg5(Gd,Y) phase→α-Mg supersatu-rated solid solution+rare earths compound Mg3(Gd1.26,Y0.74)→α-Mg supersaturated solid solution+rare earths compound Mg3(Gd0.745,Y1.255).It showed that 480 oC/4 h was the optimal solution treatment parameter.If the solution temperature was high or the holding time was long,such as 520 oC/16 h,an overheating phenomenon would be induced,which had a detrimental effect on the mechanical properties.When age-ing at 225 and 200 oC,the alloy would exhibit a significant age-hardening response and great long-time-age-hardening potential,respectively.The best mechanical properties were obtained at the parameters of 480 oC/4 h+225 oC/16 h,with the UTS of 257.0 MPa and elongation of 3.8%.
The influencing factors of surface alloying layer by evaporative pattern casting technology were investigated.A certain thickness alloying layer was formed on the surface of Mg-alloy matrix when the pouring temperature was 780°C with different vacuum degree and alloying powder size.The surface layer microstructure,micro area composition of the new phase formed on the matrix and the composition characteristics on the surface layer were examined by SEM and element scanning.The results show that the content of aluminum increases greatly on the surface layer.The micro-hardness of alloyed layer has a more obvious increase compared with that of the matrix.The size of alloying element and the vacuum degree are the key factors influencing the alloying layer,with the increase of element powder size from 0.074 to 0.15 mm and vacuum degree from 0.04 to 0.06 MPa,the surface alloying effect becomes better.
