Strain-hardenable alloys

Strictly speaking, all metals and alloys can be strain hardened. However, in the field of aluminium metallurgy, this designation is used only for alloys of those series that cannot be age-hardened. 

These alloys belong to the series 1000,3000,5000 and 8000. Their processing route is a sequence of hot forming steps, possibly followed by cold forming steps with intermediate or final annealing. 

The level of mechanical properties that can be attained depends on the alloying element. As an example, the alloys of the 5000 series that have a high magnesium content have a potential level of mechanical properties that is superior to that of alloys of the other series 1000,3000 and 8000. However, the gradual increase in mechanical strength always reaches a point beyond which any further working becomes difficult if not impossible. In this case, if further deformation is desired, it is necessary to carry out a thermal annealing treatment. 

Alloy Melting range (°C) Density, p (kg-m ) Linear expansion, (p.m-m -K 20-100°C Mass thermal capacity, c (J-kg-C-i) 0-100 °c 

Modulus of elasticity (Young s modulus), E (MPa) Temper Thermal conductivity, A at 20 °C Electrical resistivity, p (10 p.fl-m) at 20 °C 

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Plate (Fig. 10). Data for 2014-T6 plate are not available for comparison thus, the 7039-T6 and -T61 comparison for plate gauges is limited to 2219-T81 (1.0-in. plate, [ ]) and 5083-0 (annealed temper) and —HI 13 (strain hardened) from previous work and the literature p ]. Figure 10 compares the transverse tensile properties (those customarily obtained on production lots of heat-treatable alloys) of 0.75-in. 7039 plate and 1.0-in. 2219-T81 plate and the longitudinal tensile properties (those customarily used in evaluating strain-hardenable alloys) of 0.75-in. 5083 plate. 

Exfoliation also can occur in the directional fragmented grain structure of severely cold-rolled products of certain lower strength strain-hardening alloys of the AA3XXX and... 

The same applies to metallurgical tempers. A strain-hardened temper (temper HIX) will not have the same deformation capacity as a soft temper (temper O) in strain-hardenable alloys, and as an aged temper (temper T4) in age-hardenable alloys. Industrial alloys comprise... 

Magnesium Strain-hardenable alloys Increase in mechanical properties depends on 51000 (A-G3T) 5052... 

Table A.3.10. Standard conditions of annealing for strain-hardenable alloys...

The tempers of age hardenable alloys are all designated by the letter T, followed by one to five digits, the precise definition of which can be found in standard EN 515. The most common tempers are listed in Table A.3.15. As with H tempers for strain hardenable alloys, the minimum mechanical properties can be standardised. 

On the other hand, strain-hardenable alloys of the 1000, 3000 and especially 5000 series, as well as age-hardenable alloys of the 6000 series have good corrosion resistance. They can, therefore, be used without protection in many environments such as maritime environments. Many vessels in aluminium are painted on the visible parts and for decorative purposes only. Many small crafts in aluminium are not painted at all. The same is true for landing stages of marinas, road sign supports, etc. Water staining and superficial pitting corrosion do not affect the solidity of the component. 

For strain-hardenable alloys of the 1000 and 3000 series, the pitting depth is normally lower in soft tempers than in strain-hardened tempers in the latter, the pitting depth increases with strain hardening from H12 to H19. The same apphes to 5000 series alloys with a magnesium content not exceeding 3.5%. Above this concentration, a tendency to intercrystalline corrosion is observed, which increases with strain hardening. This tendency to intercrystalline corrosion can be limited by a stabilisation treatment (H3X) [13]. Alloys of the 6000 series show a resistance to atmospheric corrosion that is comparable to that of 3000 and 5000 series alloys. 

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