Aluminum Casting Heat Treatment Process
Aluminum casting heat treatment process generally includes heating, heat preservation, cooling three processes, sometimes only heating and cooling the two processes. These processes are interlinked and irreversible. Heating is one of the important processes of heat treatment of aluminum castings.
Aluminum casting heat treatment of many ways, the first is the use of charcoal and coal as a heat source, and then the application of liquid and gas fuel. The application of electricity makes heating easy to control, and no environmental pollution. With these heat sources can be directly heated, can also be molten salt or metal, as well as floating particles for indirect heating.
When the aluminum castings are heated, the workpiece is exposed to air and is often oxidized and decarburized (ie, the carbon content of the steel parts is reduced), which has a detrimental effect on the surface properties of the aluminum parts after heat treatment. Therefore, the metal should usually be in a controlled atmosphere or protective atmosphere, molten salt and vacuum in the heating, coating or packaging can also be used to protect the heating.
Heating temperature is one of the important process parameters of aluminum casting heat treatment process. Choosing and controlling the heating temperature is the main problem to ensure the quality of aluminum casting heat treatment. The heating temperature varies depending on the purpose of heat treatment of the treated metal material and the aluminum casting, but is generally heated above the phase transition temperature to obtain a high temperature structure. In addition, the transition takes some time, so when the surface of the metal workpiece reaches the required heating temperature, it must be kept at this temperature for a certain time, so that the temperature inside and outside the same, so that microstructure changes completely, this time known as the holding time. The use of high-energy density heating and surface aluminum casting heat treatment, the heating speed is extremely fast, generally there is no insulation time, and chemical aluminum casting heat treatment time is often longer.
Cooling is also an indispensable step in the aluminum casting heat treatment process. The cooling method differs depending on the process and is mainly the cooling rate. General annealing the slowest cooling rate, normalizing the cooling faster, quenching the cooling faster. But also because of different steel and have different requirements, such as empty hard steel can be the same as the normal cooling rate of hardening.
Metal aluminum casting heat treatment process can be divided into the overall aluminum casting heat treatment, surface aluminum casting heat treatment and chemical aluminum casting heat treatment three categories. Depending on the heating medium, the heating temperature and the cooling method, each category can be divided into several different aluminum casting heat treatment processes. The same metal with different aluminum casting heat treatment process, can get different organizations, which have different performance. Iron and steel industry is the most widely used metal, and steel microstructure is also the most complex, so a wide range of steel and aluminum casting heat treatment process.
The overall aluminum casting heat treatment is the heat treatment process of the metal aluminum casting which is heated as a whole and then cooled at an appropriate rate to change its overall mechanical properties. Iron and steel as a whole aluminum casting heat treatment is generally annealed, normalizing, quenching and tempering four basic processes.
Annealing is to heat the workpiece to the appropriate temperature, according to the material and the workpiece size using different holding time, and then slow cooling, the purpose is to make the internal organization of metal or close to equilibrium, access to good process performance and performance, or for further quenching Ready for organization.
Normalizing the workpiece is heated to the appropriate temperature and cooled in air. The effect of normalizing is similar to that of annealing, except that the resulting tissue is finer and is often used to improve the cutting performance of low-carbon materials and is sometimes used to Of the parts as the final aluminum casting heat treatment.