You might already know that graphite cast iron is used in sand casting and aluminum alloys are used in foundries to make the engine blocks. This is because aluminum alloys meet most of the parameters of engine blocks and weigh lower in comparison to cast iron. For the petrol engines though, engineers prefer graphite cast iron to aluminum.
Though aluminum alloys share many similarities with graphite cast iron, they are usually opted by foundry engineers for diesel engines. In die cast mold making, 319 and A356 aluminum alloys are used to make diesel engine blocks.
319 aluminum alloy has high corrosion resistance and good thermal conductivity. When molded under the T5 heat treatment process, die casters make them strong and durable. The 319 alloy has 85.8 to 91.5 percent aluminum 1 percent iron, 0.1 percent magnesium, and 1 percent zinc.
A356 aluminum alloy, on the other hand, contains 91.1 to 93.3 percent aluminum. When molded under T6 heat treatment A356 gains more strength than 319 alloys. Besides, the A356 alloy has 72.4 GPa modulus of elasticity compared to 319 alloy’s 74 GPa.
Manufacturing of Engine Blocks
Sand casting is a solidifying process that occurs in two phases known as nucleation and crystal growth. In nucleation phase, solid particles get formed inside the molten metal and they have low internal energy than surrounding liquid. Thus, below freezing temperatures are exerted due to the extra energy required to solidify. Again, the molten metal will get heated to form the crystal structures in sand casting.
Most of the casting defects may occur during the solidifying phase in sand casting and hence the quality and the strength of the sand are considered in surface finishing of the engine block.
Another method to manufacture engine blocks is die cast mold making with aluminum alloys. The die liquefies when die casters exert high temperature to the molten aluminum. The casting is then machined to get the surface finish and cooling passages, which are needed for the engine block. The pressure is applied to the mold to form them into shapes and patterns.
In engines blocks, the alloy should resist parameters such as wear and tear, combustion, temperature, and engine vibration. Aluminum alloy has more surface finishing options in die cast mold making and engine blocks are not exempt to that.