Light metals and its alloys are materials of relatively low density and high strength-to-weight ratios. These metals and alloys are of great importance in engineering applications for use in land, sea, air, and space transportation. Magnesium, aluminium and titanium are light metals of significant commercial importance. These three metals and their alloys comprise the bulk of the high strength-to-weight ratio metallic materials used in industrial systems. Aluminium is the most versatile of these materials and titanium is the most corrosion resistant with very high strength, while magnesium has the lowest density. Their densities of 1.7 (magnesium), 2.7 (aluminium) and 4.5 g/cm3 (titanium) range from 19 to 56% of the densities of the older structural metals, iron (7.9g/cm3) and copper (8.9 g/cm3). The metals commonly classed as light metals are those whose density is less than the density of steel (7.8 g/cm3, or 0.28 lb/in.3).
Since these pure metals are usually softer materials with insufficient strength, they must be alloyed to reach target mechanical properties. For example, high purity aluminium is a soft material with the ultimate strength of approximately 10 MPa, which limits its usability in industrial applications. On the other hand, tensile strength of 6061 aluminium alloy may reach more than 290 MPa depending on the temper of the material. Therefore, we are discussing primarily the alloys instead of pure metals.
Thermal Properties of Light Metals and Alloys
Thermal properties of materials refer to the response of materials to changes in their temperature and to the application of heat. As a solid absorbs energy in the form of heat, its temperature rises and its dimensions increase. But different materials react to the application of heat differently.
Heat capacity, thermal expansion, and thermal conductivity are properties that are often critical in the practical use of solids.
Melting Point of Light Metals and Alloys
Melting point of 6061 aluminium alloy is around 600°C.
Melting point of Elektron 21 – UNS M12310 is around 550 – 640°C.
Melting point of Ti-6Al-4V – Grade 5 titanium alloy is around 1660°C.
In general, melting is a phase change of a substance from the solid to the liquid phase. The melting point of a substance is the temperature at which this phase change occurs. The melting point also defines a condition in which the solid and liquid can exist in equilibrium.
Thermal Conductivity of Light Metals and Alloys
The thermal conductivity of 6061 aluminium alloy is 150 W/(m.K).
The thermal conductivity of Elektron 21 – UNS M12310 is 116 W/(m.K).
The thermal conductivity of Ti-6Al-4V – Grade 5 titanium alloy is 6.7 W/(m.K).
The heat transfer characteristics of a solid material are measured by a property called the thermal conductivity, k (or λ), measured in W/m.K. It is a measure of a substance’s ability to transfer heat through a material by conduction. Note that Fourier’s law applies for all matter, regardless of its state (solid, liquid, or gas), therefore, it is also defined for liquids and gases.
The thermal conductivity of most liquids and solids varies with temperature. For vapors, it also depends upon pressure. In general:
Most materials are very nearly homogeneous, therefore we can usually write k = k (T). Similar definitions are associated with thermal conductivities in the y- and z-directions (ky, kz), but for an isotropic material the thermal conductivity is independent of the direction of transfer, kx = ky = kz = k.
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