In: Mechanical Engineering
A cast aluminium-silicon alloy containing 12 % silicon which cannot be age hardened would normally solidify with a hyper-eutectic structure. This alloy can be used for both sandcasting and metal die-casting. Describe THREE methods in which the cast metal can be strengthened by controlling the microstructure during solidification.
Strengthing methods of cast metal by controlling the moisture during solidification:
Sand Casting: It is a process of solidifying the molten metal in a customized and pattern called mould. To define the cavity of the mould, sand is used. The molten metal is poured into this mould and solidification takes place in the mould. There are sequence of process in sand casting. The sequence is pattern making, core making, molding, melting, pouring, cleaning.
In sand casting process – moisture content in the mixture ranges from 2 to 7%. Too much moisture can cause the steam bubbles. To control the moisture in sand casting Synthetic sand to be mixed with pure sand. This composition can control the moisture and strengthen the cast metal while solidification.
Investment casting: This is a foundry process. In the process a disposable wax pattern is used to form as a mold. This wax pattern is invested into a ceramic slurry. In this process, the wax pattern get melted out at the end of the process. So, this process also called as Lox-wax casting. The sequential process involved in this casting is - Pattern making, mold making, meting, pouring, cooling, and cleaning.
Moisture can be controlled by proper drying of mould. Using dehumidifiers in investment castings reduces the drying time period, because dehumidifiers reduces the humidity of the air.
Pressure Die Casting: The name itself speaks about this process. The is a process of forcing the molten metal into a customized mold under high pressure. The mold is made from die-steel to the required shape and size as that of required component. This is expensive process because of die-steel mold. This investment casting is widely used for volume production of small to medium size components casting.
If the drying time in investment casting is lowered to short time, the moisture can be controlled. Impurities to be removed, Environmental contaminations to be controlled. These can be controlling by using the quality material under controlled process.