The characteristics and subsequent applications of each series vary considerably. For example, there are two distinct types of aluminum in the range above. They are: heat-treatable aluminum alloys (which can gain strength by adding heat) and non-heat-treatable aluminum alloys.
The 1xxx, 3xxx and 5xxx series wrought aluminum alloys are not heat treatable and will only undergo strain hardening. The 2xxx, 6xxx and 7xxx series of wrought aluminum alloys are heat-treatable alloys, while the 4xxx series includes heat-treatable and non-heat-treatable alloys. The 2xx.x, 3xx.x, 4xx.x and 7xx.x series cast alloys are heat treatable. Strain hardening is generally not suitable for castings.
Heat-treatable alloys achieve optimal mechanical properties through a process of heat treatment, most commonly solution heat treatment and artificial aging. The solution heat treatment process involves heating an alloy to a relatively high temperature (approximately 990 degrees Fahrenheit) to dissolve the alloying elements or compounds into solution. Subsequently, it is usually quenched in water, producing a supersaturated solution at room temperature.
Solution heat treatment is usually followed by aging. Aging is the precipitation of a portion of an element or compound from a supersaturated solution to obtain desired properties.
The aging process is divided into two types: aging at room temperature, which is "natural aging", and aging at high temperature, which is "artificial aging". Artificial aging temperatures are typically around 320 degrees Fahrenheit. Many heat-treatable aluminum alloys are used in welding fabrication in their solution, heat treatment, and artificial aging conditions.
Non-heat treatable alloys obtain optimal mechanical properties through strain hardening. Strain hardening is a method of increasing strength through the application of cold working.
The temper nomenclature system (see Table 3) deals with material conditions known as tempers. The temper naming system is an extension of the alloy numbering system and consists of a series of letters and numbers that follow the alloy number and are separated by a hyphen. For example: 6061-T6, 6063-T4, 5052-H32, 5083-H112.
