Cold-worked state of aluminum

Slander or cold deformation is a natural consequence of the expansion of most aluminum operations and its alloys. Sometimes it is also called the strain hardening. Hardening increases the strength of the alloy, which has been achieved as a result of doping and hardening heat treatment. For thermally hardenable alloys strain hardening may also increase the release rate of the hardening phase.

The degree of work hardening

Peening is applied to improve the strength properties of aluminum and aluminum alloy, which are not hardened by heat treatment. Sometimes these alloys - mainly alloys of series 3xxx and 5xxx – called in a positive way: strain hardened. The main "levers" for one or another cold-worked condition are the degree autofrettage – the amount of plastic deformation and annealing the cold, full or partial - heating to a temperature 350-400 ° C with a duration, usually, sufficient to fully warm up.

Full and partial annealing

Full annealing is used for the complete removal of peening material and bringing the material to a state with minimum and maximum strength characteristics plastic properties. Partial annealing is performed for a partial reduction of strength properties and increase to bring the plastic material in the finished product a predetermined state.

Symbol states aluminum alloys

To designate all states of aluminum and aluminum alloys (and not only cold-worked ones), the American notation system is widely used throughout the world, developed at the time of the American Aluminum Association.

  • The initial states of the system of notation deformable aluminum alloys is described in American Standard ANSI H35.1.
  • This system is almost "as is", adopted by the international ISO standard 2107 and European standard EN 515.
  • Domestic standards (GOST) still use their own system of state designations, which differs significantly from the international.

State of the material in the hot-pressed state without additional treatments - thermal or strain - designated standards EN and ISO the letter F and no figures for it does not follow. In this state of national standards is without any designation.

State fully annealed material designated the letter "O" (not zero) according to the international classification of states of aluminum and aluminum alloys or "M" – by domestic state standards. The letter D with additional number refers to anneal with specific conditions.

All cold-worked condition designations begin with a letter "H". Behind it can go from 1 to 3 figures.

only cold deformation – H1 series

Pure cold-worked condition without additional treatments form a series H1. Fully cold-worked condition of the material, which is designated H18, call state, obtained at cold deformation equivalent relative rolling reduction 0,75. The relative reduction - is the ratio of the difference of the initial and final sheet thickness to the original thickness of the sheet. relative hood 0,75 will be achieved, for example, at an initial thickness 10 mm and the final thickness 2,5 mm: (10 – 2,5)/10 = 0,75. H19 represents the state of the product with an even greater degree of work hardening, than in the state H18. it applies, for example, for a tape thickness 0,30 mm from an aluminum alloy 3104 for body beer cans. state H16, H14 and H12 is obtained with a smaller amount of cold deformation and represent, respectively, trichetvertinagartovannoe, polunagartovannoe and chetvertnagartovannoe states.

Standing aluminum H111 and H112

When specifying the requirements for mechanical properties of aluminum and aluminum alloys often use state designation N111 and N112 of the same series H1. N111 state differs from the annealed state of about only a small degree of work hardening, you could get the material when straightening or other technological operations. N112 state differs from the state F only a small degree of work-hardening (hot or cold working), as well as the obligatory control of the mechanical properties.

Cold deformation and annealing – series H2

H2 series refers to materials, which have been cold-worked to a higher degree, than it would have to be given to the strength properties, and then reduce this "extra" strength captured by partial annealing. With increasing degree autofrettage second digit increases from 2 to 8 similar to pure cold-worked condition: Н22, H24, N26 and N28.

The figure schematically shows a series of work-hardened state H1 and H2 at varying degrees of work hardening and annealing various durations at a constant temperature. There are similar graphs as a function of annealing temperature. In states with the same second digit ultimate strength - the same, a yield strength in states with partial annealing below, than the purely work-hardened state. Schedule a strength increase of the degree of cold deformation is convex upward. This reflects the fact, that the first step of cold deformation give maximum strength increase.

nagartovka-alyuminiya

series H3 – alloys of aluminum-magnesium

Series Н3 - states with autofrettage and stabilizing treatment: Н32, N34, H36 and N38. This series of conditions only apply for aluminum-magnesium alloys - 5xxx series alloys. The thing is, These alloys for some time in the cold-worked condition may lose, peening achieved strength properties, due to the natural aging mechanism. therefore, if the strength properties of stability is important, they are often heated to moderate temperatures, for example, 220 ° C, to complete the process of aging, thus somewhat reduced strength, but increase the flexibility and, thereby, provide subsequent mechanical stability and performance properties.

Cold deformation and varnishing – H4 series

H4 Series is used for work-hardened products with additional lacquered surface. for instance, in the manufacture of covers beer cans apply thick tape 0,26 mm aluminum alloy 5182 able to H48 – fully work-hardened and lacquered.

Standing aluminum alloys in CCITT standards

In the old, more "Soviet", but still successfully operating GOSTs apply their designations cold-worked condition. In GOST 18475-82 on the cold-tube, GOST 7871-75 the welding wire and GOST 21631-76 the following material states are provided for the sheets:

  • cold-worked (H) and
  • semi-standard (P).

In GOST 24767-81 on cold-profiles provided

  • polunagartovannoe state designation ½Н.

The relatively "fresh" GOST 13726-97 on tapes to state M and H already include additional states of the material:

  • quarter-grated (H1),
  • semi-standard (H2) and
  • three-quarter cut (H3).

designations H1, H2 and H3 have a different meaning here, than ANSI standards, EN and ISO.

GOST 18475-82 but this involves two state of the material involving work-hardening for heat-hardened alloys and AD31 1955:

  • cold-worked after quenching and artificially aged (TH) and
  • work-hardened after hardening and naturally aged (TH1).

These are analogues of international symbols T8 and T3 states, which relate to the states of a thermally hardenable aluminum alloys.