Simple Solutions That Work! Issue 17

Physical properties are an important way of distinguishing one material from another. In the study and application of metallurgy, physical properties are often considered a broader category than mechanical properties, but not all properties overlap. Physical properties are most easily distinguished from mechanical properties by the method of testing. While mechanical properties require forces to be applied to obtain a measurement, physical properties can be measured without changing the material. That said, physical properties do change in different environments. For example, most metals have a higher density at lower temperatures due to the principles of thermal expansion and contraction . Color and appearance, which are also physical properties, change based on a number of environmental factors. Physical properties of metals include: • Corrosion resistance • Density • Melting point • Thermal properties - Heat capacity - Thermal conductivity - Thermal expansion • Electrical conductivity • Magnetic properties WHAT IS AN ALLOY? The word alloy appears throughout the Eagle Group Blog, especially here in this series. An alloy is a uniform mixture made from a combination of individual elements, when at least one of the elements is a metal. Common alloys include bronze, which is a mixture of copper (Cu) and tin (Se). Steel is a mixture of iron (Fe) and carbon (C), and stainless steel includes other alloying agents like chromium (Cr), nickel (Ni) and manganese (Mn). CORROSION RESISTANCE Many types of corrosion can occur. Corrosion is a process in which a material is reduced to a more stable state via chemical reaction, often related to the atmosphere or service conditions. Rust, a common sight on unprotected products made of ferrous metals, is one of the most common forms of corrosion. Corrosion resistance , on the other hand, is the material's ability to resist the reaction to move toward a more stable state in its environment. Raw aluminum, silicon, titanium and their alloys are naturally corrosion resistant due to an unreactive layer that quickly forms on their surfaces. A common alloy for many applications requiring corrosion resistance is stainless steel. Unlike carbon steel, stainless steel alloys are able to resist surface corrosion when exposed to environments that would normally cause corrosion, including wet, acidic or high heat. DENSITY The density of an object is determined by a simple formula: the object’s mass (M) divided by its volume (V). At first, the practical application of density was to determine the authenticity of gold, as in the story of the golden crown. Gold is an excellent candidate for testing density, because it is a much denser material than other metals, with an average density of 1,206 lbs. per cubic foot. Alloys more commonly used in manufacturing have lower densities. Steel averages around 494 lbs./ cubic foot, while stainless steel is a bit less. Titanium is about half the density of steel, and aluminum is about one-third. Practically speaking, this means that a part made of steel will weigh approximately three times more than the exact same part made of aluminum. OVERVIEW OF PHYSICAL PROPERTIES OF METALS 4 By Jason Bergman Senior Quality Engineer and Metallurgist at Eagle Alloy