Heat Treatment Of Casting

• Solution treatment:

Solution heat treatment involves heating an alloy to a suitable temperature, holding at that temperature long enough to allow one or more constituents to enter into solid solution and then cooling rapidly enough to hold the constituents in solution.

• Solution homogenization treatment

1)      It is used to minimize or eliminate the concentration differences the segregation which occurred during solidification of an alloy.

2)      Improves corrosion resistance of the castings.

3)      Improves casting ductility especially in ingots required to be worked later on.

4)      Makes an alloy amenable to subsequent hardening treatment.

Solution heat treatment is carried out for aluminium, magnesium and copper base alloys.

1)      Since solution heat treating temperature are generally not for below the melting point of the alloy, great care should to be taken to control the furnace temperature to the desired value. Temperature higher than required may tend to start melting of the casting.

2)      Solution treatment temperature should be held within +_10f because rate of diffusion (of CuAl2) rapidly decreases with decreasing temperature.

3)      Solution heat treating furnace equipment should work accurately and provide uniform temperature.

• Precipitation treatment or ageing:

Ageing: produces a change in the properties of a metal or alloy at a slow rate at room temperature and more rapidly at higher temperature. Changes in the properties are produced with the passage of time at normal temperature.

• Age hardening: it is hardening by ageing, usually after rapid cooling or cold working.

• Precipitation treatment: it is artificial ageing in which a constituents precipitates from a supersaturated solid solution.

• Precipitation hardening;

It is hardening caused by the precipitation of a constituents from a supersaturated solid solution.

The precipitation of the constituents is a low temperature time dependant change is usually employed for strengthening.

Ageing may be carried out at room temperature or at a elevated temperature of the order of 300 to 400 f depending upon the alloy.

As that of solution heat treatment, temperature control of ageing cycle is also necessary.