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How Hot Is Too Hot For Aluminum?

How Hot Is Too Hot For Aluminum?
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Aluminum is an amazing metal with outstanding mechanical properties that make it an ideal choice for a variety of applications. One of the qualities that sets it apart from other materials is its thermal conductivity. Of all the commonly used metals, copper and aluminum have the greatest thermal conductivity, making aluminum a great option for tasks that involve regulating or moving heat.

While certain aspects of aluminum tend to get all the attention, such as it’s high strength to weight ratio, excellent corrosion resistance and extreme formability, thermal conductivity often gets overlooked. With the ability to conduct heat much greater than stainless steel and other metals, aluminum has become a great option for manufacturers in many industries, including electronics, plastics and aerospace.

One of the questions we often get asked is how hot can aluminum get before it becomes a problem. People want to know how much heat can be applied to aluminum parts and machinery before the material fails. What these questions all come down to is two main principles: thermal conductivity and melting point; that’s what we’ll be discussing today.

How do we measure thermal conductivity?

What we mean when we talk about a material’s thermal conductivity is its ability to conduct heat. In scientific terms, this is specified as a number based on what is known as Fourier’s law, which states that the rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area, at right angles to that gradient, through which the heat flows. This is a complicated way of saying that thermal conductivity tells us how fast heat gets transferred through material. In general, the higher the number, the faster the heat transfer.

It’s also important to note that even with pure aluminum, the actual number varies depending on the amount of heat; calculating conductivity can be even more complicated with various alloys. You should never assume that the lab number for thermal conductivity is correct, as you will need to test your application in a variety of scenarios to be sure of how it handles various temperatures.

Let’s look at some real world examples. Styrofoam, which is often used as an insulating material, has very poor thermal conductivity. A Styrofoam cup is good for holding hot coffee because it does not allow the heat of the liquid to transfer to your hand holding the cup. On the other hand, a metal like aluminum has excellent thermal conductivity. That means that if you had an aluminum cup filled with extremely hot coffee, the cup itself would be hot to the touch and hard to hold onto.

A heat sink refers to a passive heat exchanger in which heat generated by an electronic or mechanical device is transferred to either the air or a liquid coolant, thereby preventing the device from overheating. A common use for heat sinks is in CPUs and GPUs, which tend to run hot and which can be damaged by excess heat. Aluminum is commonly found in such devices thanks to its thermal conductivity and light weight.

Another industrial application that benefits from aluminum’s high thermal conductivity is plastics processing. When melted plastic is solidified into a finished part through the injection molding or blow molding process, the curing time in the mold is dependent on the thermal conductivity of its material. Using aluminum instead of steel reduces the cycle time to make the part, increasing productivity and reducing valuable press/machine time.

What is aluminum’s melting point?

Of course, this thermal conductivity is only good to a point. If metal is heated too much it will start to deform, so it’s essential that you know your material’s melting point and how much heat it will need to withstand before using it in an application. There are other situations where knowing aluminum’s melting point is essential, such as when welding or heat treating an aluminum alloy.

What is aluminum’s melting point? If you look it up in a textbook the answer will be 1,221°F (660.3°C), but manufacturers almost never work with pure aluminum. Every alloy has a different melting point, and some are created specifically to thrive in high temperature environments. There are high strength aluminum alloys with Zn, Mg, Cu and Sc as alloying elements that have a melting point as high as 1275°F.

On the other hand, it’s necessary to realize that melting point is not the only factor that must be considered when trying to understand how a metal will handle high temperatures. For example, if you weld an aluminum work piece using 5356 aluminum alloy as weld rod, then the finished part would be highly susceptible to stress corrosion cracking at as little as 150 degrees. The same is true of 5183 and 5556 aluminum alloys. While the melting point might never be reached, you need to be aware that other problems can occur when some alloys are exposed to even moderately high temperatures.

Another major concern with high temperature applications of aluminum is the point at which the mechanical properties of the metal will be affected. Richly alloyed grades that have been strengthened by heat treatment processes will lose these higher mechanical properties when exposed to elevated temperatures. Exposure to excessive heat will temper back and weaken the heat treated metal.

If you have an application that will experience high heat, it’s important that you carefully test it in the prototyping stage, especially if durability is an important consideration. Selecting the right alloy that will perform correctly under your particular set of conditions is imperative to ensuring your bottom line. That’s why working with an experienced material provider can help save you both time and money.

Your Technical Resources Provider

Distinguishing between the many different and diverse aluminum alloys available on the market today isn’t easy. At Preferred Alloys, we pride ourselves on working closely with our clients to match the right material to every application. Our goal is to be more than just a supplier but a full technical resources partner. We strive to help each of our customers to extract the maximum value from their purchasing decisions.

That’s made possible because our staff averages nearly 13 years of working for us. For this reason and others, Preferred Alloys has become the Midwest’s leading supplier of aluminum and stainless steel products. Contact us today to learn more about which aluminum alloy is right for you; we’ll help you answer the question of how much heat is too much heat.

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