In one of my previous article, I extensively discuss on heat treatment of ferrous and nonferrous metals, their processes were also explained. Today I will be discussing on how aluminum is heat treated.
Let me recall your memory on the definition of heat treatment. Heat treatment is said to be a metal working process of changing physical and sometimes chemical process of a metal.
Just as promised to explain the nonferrous metal mentioned.
Heat treatment of aluminum and aluminum alloys:
Heat treatment of aluminum is carryout in order to increase the strength and hardness of a certain subset of aluminum alloys that are hardened by precipitation.
Different requirement of an aluminum properties leads to various heat-treating process. they are, homogenizing, annealing, solution heat treatment, natural aging, and artificial aging.
Annealing – aluminum alloys obtain strain hardening when subjected to work. It occurs when the material is plastically deformed, which causes the grain structure within the aluminum to slide against each other along the slip plane area. The purpose of such aluminum alloys is to restore the crystalline grain structure and the slip plane. Helping the continuation of the shaping with low force. In other words, to relieve internal stresses that is develop during operation, such as cold forging or casting.
Annealing is achieved on aluminum alloys when the material is heated at about 570-degree Fahrenheit to 770-degree Fahrenheit, which is for about 30 min to 3 hours. The temperature and time is determined by the composition of the alloys and the size of the material. The rate of cooling is not critical. That is, it has no effects after the annealing process is achieved.
Homogenizing – homogenizing is done to distribute the precipitation elements more evenly in an aluminum part. It is achieved by raising its temperature below its melting point, usually between 900-degree Fahrenheit to 1000-degree Fahrenheit. If the homogenizing temperature reaches, the aluminum is allowed to slowly cool.
Solution heat treatment – the purpose of solution heat treatment is to allow the metal part to be easily work. It is performed by heating the aluminum part at a specific temperature, depending on the alloy composition in the aluminum. Specifically, at the range of 825-degree Fahrenheit to 980-degree Fahrenheit. If the exact temperature is obtained, the operation will not be successful. That is, if the temperature is too low, there will be strength lost, and when the temperature is too high, then the part could melt, end up been discolored. Or increased strain within the part. The part is soak when it reaches the target temperature. this soaking time can be from 10 min for then materials to 12hours for longer or thicker parts. The part is quenched at this point. The quenching or rapid cooling help to preserve the final distribution of dissolve elements in the alloy that was achieved. that is, to “freeze” the trapped elements in place, or to cool the aluminum part rapidly enough to keep the alloying element to precipitate out as the part cools. The part is commonly cooled with water.
Natural aging – aluminum that undergoes solution heat treatment will precipitate out after some time, which will cause the grain to look into position, helping to increase the natural strength of the part. Natural aging or age hardening process take place at room temperature within four to five days, obtaining at least 90 percent of the hardening within the first day. With this reason aluminum materials are shaped rather quickly after it undergo solution heat treatment.
Artificial aging (precipitation hardening) – artificial hardening is done when an aluminum part needed maximum hardness, which is not achieved during natural aging, at room temperature. in order to achieved this, the dissolved elements need to be fully precipitate out, which is done by subjecting aluminum to heat to an alloy at a specific temperature. usually at 240-degree Fahrenheit and 460-degree Fahrenheit of exact temperature. at this point, it is soak for about six to twenty-four hours, and then cooled at room temperature. the aluminum part will then increase in the yield strength, little increase in tensile strength, and decrease in ductility.
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Heat treatment of aluminum and copper undergoes almost the same heat-treating process. but they their result is definitely different. The process annealing, homogenizing, solution heat treatment can be performed on copper and aluminum giving different result. Just as explained, annealing is carried out in copper to soften the materials that has been work hardened. Whilst on aluminum, it is done to achieved strain hardened material, unlike copper that losses its hardening (strain hardening) when annealed. Same occurs on homogenizing.
And that is it for this article, heat treatment of aluminum and aluminum alloys. I hopefully believed you’ve gain a lot from this article. You can ask question via comment box and please don’t forget to share. Thanks for reading!
Question: in your own understand, briefly explain how aluminum is heat treated.