Al-15Si-6Ni Abstract: In the conventional common crystal Al-Si alloy centrifugal casting, the primary Si particles, pores and slag will converge in the inner layer at the same time, reducing the strengthening effect of Si particles in the enhancing layer. In order to avoid this disadvantage, use Al-15%Si-6%Ni as the blank, and successfully prepare the gradient mixture of the particles, pores and slag in the inner layer. The analysis of multiple samples under different process parameters shows that in the centrifugal force field, the particles will push the less dense primary crystal Si particles to the outer layer together, forming a gradient composite material with high volume fraction in the outer layer. The application of the electromagnetic field effectively reduces the adhesion and agglomeration of the primary particles and refines the grains.(1) Each sample has different degrees of pores and slag clips. The pores and slag in the casting mainly come from the curgas and oxidation in the centrifugal forming process. With the solidification of the casting, the involved gas precipitation, due to its small density, will be biased to the inner layer of the cast together with the slag, thus forming a defect layer in the innermost region, as shown in the d and e regions shown in Fig.(2) The intervention of the magnetic field is conducive to reducing the adhesion of the particles. As shown in Figure Figure 4-1, the particles clearly show an agglomeration shape without a magnetic field. With the intervention of the magnetic field and the increase of the magnetic field, the agglomeration of particles decreases significantly, as shown in Figure Figure 4-2,4-3,4-4. (3) The particles show a tendency of polarization to the outer layer. Under the centrifugal force, the particles showed a clear trend of polarization toward the outer layer, and with the centrifugal speed, regions a, b, c in Figure 4-5,4-3,4-6,4-7,4-8.(4) Separation of the particle enhancement area from the defect area. The outer layer (a, b, c area) of the casting is called the particle enhancement area because of large particles; the inner layer of the casting (d, e area) contains a lot of pores, slag and small particles, which is called the defect area.
2.3 Effect of magnetic field on microscopic organization Figure 7-9 are typical microscopic organization of sample layers at 1000 r/min and current intensity at 0, 1.5A and 2A. Among them, there are black block, Si and light gray bars, block block, NiAl3 and white α -Al tissue. Primary crystal, Si and NiAl3 largely gather, adhere and wrap together with each other. When there is no external magnetic field (i. e., current 0), the initial Si of the outer sample is smaller, the initial Si of the inner layer is larger than the outer layer, the size of the middle transition layer particles is between the inner and outer layers, the primary Si particles are mainly block in each layer, and the primary NiAl3 particles are not obvious in each layer, mainly block and long strips of different sizes. After adding magnetic field, the Si and NiAl3 of each layer of the sample were refined to different degrees. When the magnetic field strength is small (current 1.5A), the primary crystal Si particles become smaller, changing from sharp block to round block. The primary crystal NiAl3 is also refined to varying degrees, and the block becomes smaller, and the long strip are broken into blocks. When the magnetic field strength is large (current 2A), the primary Si and NiAl3 of each layer are no longer refined, and even the primary Si and NiAl3 particles become larger, the primary Si blocks become larger, and the primary NiAl3 strips become more large.
