Effect Of Casting Processes And Electromagnetic Field On The Size And Distribution Of Primary Si In DC Casting A390 Aluminum Alloy Hollow Billets

Hypereutectic Al-Si aluminum alloy is regard as one of the first choices for automobile engine cylinder liner materials, and does process wide application prospect. Hypereutectic Al-Si alloy castings, however, always contain coarse primary Si and serious primary Si segregation, so their mechanical properties have been greatly reduced. In order to solve those problems, A390 aluminum alloy have been studied. The solidification structures of A390 aluminum alloy hollow billets with the size of Φ214mm/Φ60mm,Φ164mm/Φ60mm, Φ144mm>Φ60mm have been observed, then the effects of modificators, casting processes and electromagnetic field on the macroscopic distribution and average size of primary Si have been investigated, and the conclusions are as follows:(1) With the application of single modifier of P, the results show that the Al-P master alloy provides better modification effects than Cu-P master alloy. In addition, P-Y compound midifier provide better modification effects than P single modifier. Further, when 0.03wt% Y is added into the alloy during casting, the primary Si can be refined apparently, and the average size of the primary Si is 25.10μm, meanwhile the macroscopic distribution homogeneity of primary Si is the best.(2) During the DC casting of A390 aluminum alloy hollow billets, as the outer diameter decreases, and the corresponding casting speed increases, which lead the cooling rate of the alloy melt to increase during solidification. Results show that the primary Si can be refined remarkably and distribute more uniformly by the increase of cooling rate.(3) During the DC casting of A390 aluminum alloy hollow billet (Φ164mm/Φ60mm), with the casting temperature increases, the average size of primary Si decreases, moreover, the primary Si distributes more uniformly, which lead to the conclusion that the primary Si can be refined remarkably and distribute more uniformly by the increase of casting temperature.(4) When the low frequency electromagnetic field are added to DC casting, the distribution of primary Si doesn’t change apparently; and after the electromagnetic vibration and DC magnetic field are applied to the DC casting, thick Si-poor layer is likely to form, which will aggravate the macroscopic segregation of primary Si; however, with the application of rotating magnetic field, the distribution homogeneity of primary Si in A390 hollow billet is refined effectively. When introducing low frequency electromagnetic field or electromagnetic vibration in to the DC casting, the average size of primary Si decreases, namely the primary Si can be refined obviously. On the contrary, DC magnetic field and rotating magnetic field don’t have positive effect on the grain refining of primary Si.(5) The size and distribution homogeneity of primary Si doesn’t change apparently with the process of extrusion, and it is the original solidification structures of A390 aluminum alloy that have crucial function on the size and distribution of primary Si.