PHYSICAL & MECHANICAL PROPERTIES - INTRODUCTION

There is a very large range of METAL/ALLOY materials for artists and designers to select from, so it obviously helps to categorise the characteristics of these often quite different materials, to help make informed choices about which is the best choice of material for particular project. In other words we can use the common properties of metals for comparative and selection purposes.

The common properties of every ELEMENTAL METAL is definitively known, for instance IRON (Fe), which was earlier used as an example in the topic: SOLID TO LIQUID & BACK AGAIN, has a MELTING POINT  of 1536°C and a BOILING POINT of 2860°C. This data can be directly compared that of COPPER (Cu), which has a melting point of 1085°C and boiling point of 2560°C. From this information we know that if we want to melt either of these metals together to make a WELDED JOINT, then we will need welding equipment that will be capable creating these temperatures. We can also compare other data such as DENSITY (Fe: 7.87 g/cm³ - Cu: 8.96 g/cm³), or HARDNESS (Fe: BRINELL HARDNESS NUMBER (BHN) 66 – Cu: BHN 48). These examples and other comparative data allow designers to refine their search for an optimum material.

Things become rather more complicated when we want to compare an ELEMENTAL METAL with an ALLOY, or alternatively, one type of alloy with a quite different alloy. For example, we cannot compare STEEL (an alloy of IRON), with BRONZE (an alloy of COPPER) in quite the same way as we could for their elemental parent metals. Firstly, 'STEEL' and 'BRONZE' are both generic descriptions which encompass a vast range of materials, often with radically different properties (even within their respective alloy groups). For example softer grades of LEADED BRONZE have a hardness rating in the region of BHN 45; whereas high strength ALUMINIUM BRONZE has a rating in the region of BHN 170. [ref 1] The BHN hardness range for LOW CARBON (mild) STEELS generally falls between BHN 150-205. [ref 2] The conclusion that can be drawn here is that LCS is typically a harder material than BRONZE, but there are significant exceptions.

These examples illustrate how difficult it is to accurately compare the properties of alloy groups unless each alloy grade is specified in detail and a certain amount of accurate data is known - sweeping generalisations about alloys can be very misleading.

Data on a metal product’s properties can also provide the user with an indication of how the material might behave when worked in a particular manner or used in a particular application. Information on PLASTICITY for example, can help determine how easy it would be to fold a sheet of metal in a BRAKE PRESS, the opposite of plasticity is BRITTLNESS, brittle material folded in a brake press would be prone to fracturing or even shattering whilst being worked, on the other hand a material that is too MALLEABLE and prone to CREEP might not hold it’s folded form over any length of time.

The following section lists some of the important physical and mechanical properties of metals, with some general information on how these properties relate to fine art, architectural detail and design uses.

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