High-strength and high-thermal conductivity new material composite brake drum and preparation method thereof

A method for preparing a high-strength and high-thermal conductivity new material composite brake drum, wherein, the high-strength and high-thermal conductivity new material composite brake drum comprises an outer layer and an inner layer, the outer layer is made of high-strength ductile iron, the inner layer is made of low-alloy gray cast iron, and the outer layer and the inner layer are fused together by means of solid-liquid bonding, the preparation method is as below:

• 1) Smelting molten iron, and after the molten iron is melted, adding 1-1.5% by weight of rare-earth ferrosilicon magnesium spheroidizing agent and 0.8-1.3% by weight of ferrosilicon inoculant at a bottom of a ductile iron ladle for spheroidization while keeping the spheroidization temperature at 1560-1650° C.;
• pouring the spheroidized molten iron into cavities from a pouring cup at a pouring rate of 15-25 seconds for each cavity while controlling the pouring temperature at 1420-1480° C. for a total pouring period of ≤15 minutes;
• after the molten iron is completely solidified and when the temperature drops to 950-1000° C., taking it out of the cavities and cooling in air to a temperature of 280-360° C., degating, grinding and cleaning sand to obtain a high-strength ductile iron outer casting of the composite brake drum;
• 2) Placing the outer casting on a centrifuge, adding a compounding agent to a part of an inner surface that needs to be compounded with gray iron, heating the inner surface rapidly to 770-820° C.;
• then pouring the inner layer at a pouring rate of 5-12 seconds for each brake drum at a pouring temperature of 1410-1445° C. while keeping the rotating speed of the centrifuge at 550-600 rpm;
• during the pouring of molten iron in the inner layer, adding SiC of 250-300 meshes along with the molten iron stream at an amount accounting for 3.8-4.3% by mass fraction of the molten iron entering the outer casting;
• and during the centrifugal pouring of the molten iron, adding an electromagnetic field with a magnetic field strength of 0.15-0.25 T;
• turning off the electromagnetic field 1 minute after all the molten iron enters the outer casting;
• then raising the rotating speed of the centrifuge to 1050-1100 rpm, and cooling a shell of the outer casting by spraying;
• after the molten iron is completely solidified, reducing the rotating speed of the centrifuge to 100-120 rpm, and bringing the temperature down to 500-580° C., stopping spray cooling and shutting down to take out the outer casting and the solidified inner layer, which is finished to obtain the high-strength and high-thermal conductivity new material composite brake drum;
• wherein, in step 2), the inner layer is made of low-alloy gray cast iron, and the chemical composition of the molten iron as well as mass fractions thereof are controlled at:
• 3.21-3.75% C, 1.30-2.14% Si, 0.52-1.09% Mn, 0.21-0.48% Cr, ≤0.10% S, ≤0.06% P, the balance Fe.