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Metal Glossary


Hall Heroult Process, Smelting

The main process used for the production of Aluminium metal whereby Alumina is dissolved in a salt bath of molten cryolite and subject to an electrolysis process. Often referred to as Smelting, this process uses very large amounts of electricity. Named after two scientists who developed the process independently of each other at around the same time.


Hall-Heroult Process

The main process used for the production of Aluminium metal whereby Alumina is dissolved in a salt bath of molten cryolite and subject to an electrolysis process. Often referred to as Smelting, this process uses very large amounts of electricity. Named after two scientists who developed the process independently of each other at around the same time – Hall, English and Heroult, French.

Related terms: Smelting


Hardness Test

A test conducted to measure Hardness. A load is applied to an indenter to press it into the surface of the test piece. The indenter can be either a ball of various standard diameters or a diamond of one of several specified geometric profiles. The result of the test is reported as a Hardness Number which is derived from either a measurement of the depth to which the indenter penetrates or from the surface area of the impression left by the indenter.

Related terms: Hardness


Hardness, Brinell Hardness, Rockwell Hardness, Vickers Hardness

The resistance of a metal to plastic deformation usually by indentation using a diamond or a hardened steel ball. There are various recongnised hardness scales including Vickers (VPN), Brinell and Rockwell. N.B. The empirical, but robust, relationship between hardness and tensile properties that applies in steels does not apply, and the steel tables must not be used for aluminium and its alloys. A less rigorous relationship has been established for some aluminium alloys but it is not widely used.


Heat Treatable Alloy

Any of the 2xxx, 6xxx, 7xxx and 8xxx series of wrought aluminium alloys whose mechanical properties can be increased by a solution treatment and age hardening heat treatment cycle.


Heat Treatment

The thermal processing of a work-piece specifically to alter its mechanical properties. It includes:- 1. Annealing to soften and improve ductility. 2. Solution treatment and precipitation hardening to increase strength. It does not include heating before hot rolling, forging or extrusion etc.


Heat, Cast, Melt

These terms are used interchangeably to refer to the product of a single melting furnace charge. Sometimes the furnace contents are tapped into two or more ladles when the product of each ladle may be called a separate cast. It is always assumed that the chemical composition of an entire cast will be uniform. This is described as the “cast analysis” on a Certificate of Conformity etc.


Homogenistation

The structure of as cast semi finished products e.g. slab, extrusion billet or forging blanks is invariably chemically segregated - that is the alloying elements are concentrated locally rather than uniformly distributed within the microstructure. Homogenising is a way of mitigating this as the work-piece is held at a suitably high temperature for sufficient time to eliminate, or at least decrease, chemical segregation by diffusion of the alloying elements.


Hot Working

Plastic deformation, e.g. hot rolling, extrusion or forging, of a work piece in a temperature range and at a rate such that strain hardening does not occur.