Heat treating is used as a aluminum alloy casting second process, with T5 and T6, after the initial casting phase. This process is used to improve the mechanical and physical properties of an aluminum casting part. This process consists of the heating and cooling of a aluminum casting, which does not change or affect the shape of a casting. This will greatly improve the aluminum cast part’s strength, hardness and electrical conductivity. In addition, Heat Treating also improves the finish machining of a aluminum castings.
Continuous heat treatment furnace, that is to say, all heat treatment processes are completed in the furnace at one time, and there are visual control such as specified pressure and temperature of each stage. Usually, it takes three days to heat treat general parts.
There are several steps during the aluminum heat treatment process:
Preheating / Holiding- heating – The first thermal operation applied to aluminum ingots prior to hot working. The main objective of preheating is greatly improved workability. Homogenizing allows for the reduction or elimination of chemical segregation and dendritic structures within a aluminum cast part. Heating is one of the important processes of heat treatment. There are many heating methods for metal heat treatment. The first use of charcoal and coal as a heat source, and then the use of liquid and gaseous fuels. Electrical applications make heating easy to control and environmentally friendly. These heat sources can be used for direct heating, or by indirect heating of molten salts or metals, or floating particles.
When the metal is heated, the workpiece is exposed to the air, and oxidation and decarburization (ie, the carbon content on the surface of the steel part) often occur, which has a detrimental effect on the surface properties of the parts after the heat treatment. Thus, the metal should generally be heated in a controlled or protective atmosphere, in a molten salt and in a vacuum, or protected by a coating or packaging process.
Heating temperature is one of the important process parameters of the heat treatment process. Selecting and controlling the heating temperature is the main problem to ensure the quality of heat treatment. The heating temperature varies depending on the metal material to be treated and the purpose of the heat treatment, but is generally heated above a certain characteristic transition temperature to obtain a high temperature structure. In addition, the transformation takes a certain time, so when the surface of the metal workpiece reaches the required heating temperature, it must be kept at this temperature for a certain period of time, so that the internal and external temperatures are uniform, and the microstructure is completely transformed. This period of time is called the holding time.
Annealing – This heat treating operation will remove stresses or soften the material for improved machining response, change physical or mechanical properties and can produce a defined structure..Annealing is a metal heat treatment process that refers to slowly heating a metal to a temperature for a sufficient period of time and then cooling at a suitable rate. The purpose is to reduce hardness, improve machinability, reduce residual stress, stabilize size, and reduce deformation and cracking tendency.
Purpose of annealing:
(1) Reduce hardness and improve machinability.
(2) Reducing residual stress, stabilizing the size, and reducing the tendency of deformation and cracking;
(3) Refine the grains, adjust the structure, and eliminate tissue defects.
(4) Uniform material organization and composition, improve material properties or prepare for later heat treatment.
Hardening / Quenching – Hardening through water-quench, oil-quench, forced-air quench or still-air quench will result with improved mechanical properties, toughness and hardness of the aluminum alloy structure.
Cooling is also an indispensable step in the heat treatment process. The cooling method varies from process to process, mainly to control the cooling rate. Generally, the annealing rate is the slowest, the normalizing cooling rate is faster, and the quenching cooling rate is faster. However, there are different requirements depending on the type of steel/aluminum. For exampl, part in A356, usually cooling station need 6-12H, of course, its basing on actual structure.
In conclusion, our combination of first class heat treating equipment and personnel provide effective heat treatment services. aluminum Castings Tangsheng has the capability to provide many different types of treatment options for our customers.