The following description is about the basic knowledge of Al/Aluminum Alloys.
Tag 1: Nomenclature of Al Alloys
1xxx => Pure Al
2xxx => Cu Heat Treatable
3xxx => Mn
4xxx => Si
5xxx => Mg
6xxx => Mg, Si Heat Treatable
7xxx => Zn Heat Treatable
8xxx => Other elements
Tag 2: Forging
The forging of aluminum alloys is the process of converting a uniform blank shape into a final product by hammering the material between shaped or flat dies. This working process may take place in one stage or several stages. The great majority of aluminum forgings are made in the heat-treatable alloys, but forgings in pure aluminum and in some of the non-heat-treatable alloys find application in certain fields. The precision forgings are used for many highly stressed parts, such as in aircraft undercarriage gear, internal combustion engines and other power units. Forged components have an advantage of near net shape, minimized further machining.
Tag 3: Quenching
This is a critical operation and must be carried out to precise limits if optimum results are to be obtained. The objective of the quench is to ensure that the dissolved constituents remain in solution down to room temperature.The speed of quenching is important and the result can be affected by excessive delay in transferring the work to the quench. The latitude for the delay is dependant on section and varies from 5 to 15 seconds for items of thickness varying from 0.4mm to 12.7mm. Generally, very rapid precipitation of constituents commences at around 450°C for most alloys and the work must not be allowed to fall below this temperature prior to quenching.
Another factor to be considered in quenching is the work load and the ability of the quenchant to extract the heat at sufficient rate to achieve the desired results.The usual quenching medium is water at room temperature. In some circumstances slow quenching is desirable as this improves the resistance to stress corrosion cracking of certain copper-free Al-Zn-Mg alloys.Parts of complex shapes such as forgings, castings, impact extrusions and components produced from sheet metal may be quenched at slower quenching rates to improve distortion characteristics.Thus a compromise must be considered to achieve a balance of properties in some instances. Quenchants used in slower quenching applications include water heated to 65-80°C, boiling water, aqueous solutions of polyalkalene glycol or forced air blast.
Tag 4: Annealing
Annealing is applied to both grades to promote softening. Complete and partial annealing heat treatments are the only ones used for the non-heat treatable alloys. The exception is the 5000 series alloys which are sometimes given low temperature stabilisation treatment and this is carried out by the producer.
Annealing is carried out in the range 300-410℃ depending on the alloy. Heating times at temperature vary from 0.5 to 3 hours, conditional on the size of the load and the alloy type. Generally, the time need not be longer than that required to stabilize the load at temperature. Rate of cooling after annealing is not critical.
Where parts have been solution heat-treated a maximum cooling rate of 20℃per hour must be maintained until the temperature is reduced to 290℃.Below this temperature, the rate of cooling is not important.
Tag 5: Melting