Work Hardening Aluminum Alloys: Part One

요약:

Strain hardening is a natural consequence of most working and forming operation aluminum and its alloys. In pure aluminum and the non-heat-treatable aluminum-manganese and aluminum-magnesium alloys, strain hardening increases the strengths achieved through solid solution and dispersion hardening. In heat treatable alloys, strain hardening not only supplements the strengths achieved by precipitation but also increases the response to precipitation hardening.
Work hardening is used extensively to produce strain-hardened tempers of the non-heat-treatable alloys.

Strain hardening is a natural consequence of most working and forming operation aluminum and its alloys. In pure aluminum and the non-heat-treatable aluminum-manganese and aluminum-magnesium alloys, strain hardening increases the strengths achieved through solid solution and dispersion hardening. In heat treatable alloys, strain hardening not only supplements the strengths achieved by precipitation but also increases the response to precipitation hardening.

Work hardening is used extensively to produce strain-hardened tempers of the non-heat-treatable alloys (Table 1). The severely cold worked or full-hard condition (H18 temper) is usually obtained with cold work equal to about 75% reduction in area. The H19 temper identifies products with substantially, higher strengths and greater reductions in area. The H16, H14, and H12 tempers are obtained with lesser amounts of cold working, and they represent three-quarter-hard, half-hard, and quarter-hard conditions, respectively.

A combination of strain hardening and partial annealing is used to produce the H28, H26, H24, and H22 series of tempers; the products are strain hardened more than is required to achieve the desired properties and then are reduced in strength by partial annealing. A series of strain-hardened and stabilized tempers -H38, H36, H34, and H32 -are employed for aluminum-magnesium alloys. In the strain-hardened condition, these alloys tend to age soften at room temperature. Therefore, they are usually heated at a low temperature to complete the age-softening process and to provide stable mechanical properties and improved working characteristics.

Products hardened by cold working can be restored to the O temper, a soft, ductile condition, by annealing. Annealing eliminates strain hardening, as well as the changes in structure that are the result of cold working.

Table 1. Temper Designations for Strain-Hardened Alloys

Temper Description
F As-fabricated.
No control over the amount of strain hardening; no mechanical property limits.
O Annealed, recrystallized. Temper with the lowest strength and great- est ductility.
H1 Strain hardened.
H12, H14, H16, H18. The degree of strain hardening is indicated by the second digit and varies from quarter-hard (H12) to full- hard (H18), which is produced with approximately 75% reduction in area.
H19. An extra-hard temper for products with substantially higher strengths and greater strain hardening than obtained with the H18 temper.
H2 Strain hardened and partially annealed.
H22, H24, H26, H28. Tempers ranging from quarter-hard to full- hard obtained by partial annealing of cold worked materials with strengths initially greater than desired.
H3 Strain hardened and stabilized.
H32, H34, H36, H38. Tempers for age-softening aluminum-magnesium alloys that are strain hardened and then heated at a low temperature to increase ductility and stabilize mechanical properties.
H112 Strain hardened during fabrication.
No special control over amount of strain hardening but requires mechanical testing and meets minimum mechanical properties.
H321 Strain hardened during fabrication.
Amount of strain hardening con- trolled during hot and cold working.
H321 Strain hardened during fabrication.
Amount of strain hardening con- trolled during hot and cold working.
H323, H343 Special strain hardened, corrosion-resistant tempers for aluminum- magnesium alloys.

The deformation of aluminum and its alloys proceeds by normal crystallographic slip processes. Evidence of such slip can be seen in single crystals and coarse-grained materials if surfaces are polished metallographically before deformation.

More severe cold working produces even higher dislocation densities and a further reduction in fragment size. The lattice distortions associated with the dislocations and interaction stresses between dislocations are the principal sources of strain hardening resulting from cold work.

Cast aluminum tends to have a random distribution of grain orientations, except where columnar grains are formed. The random character of the cast structure is rapidly lost during hot or cold working; it is replaced by crystallographic "textures", in which considerable numbers of the grains and grain fragments assume, or approach, certain orientations. Such textures are caused by slip on restricted crystallographic planes and in certain crystallographic directions. At room temperature, slip occurs on the {111} planes in the (110) directions. Deformation on sets of such planes produces a gradual rotation of grains and grain fragments into specific orientations with respect to the surface of the workpiece and the direction of working.

The final textures achieved with large amounts of deformation vary with the nature of the working process, with the changes in shape of the workpiece, and, to a lesser extent, with the composition of the alloy. Aluminum wire, rod, and bar usually have a "fiber" texture, in which a {111} direction is parallel to the axis of the product, with a random orientation of crystal directions perpendicular to the axis. In rolled sheet, the deformation texture may be described as a mixture of the more textures.

Although aluminum is usually considered to be an isotropic material, the textures developed by various working practices produce some directionality in properties. Generally, this directionality is much less than that observed in hexagonal metals and in some other cubic metals. The principal problem associated with directionality in strain-hardened aluminum alloys is the formation of ears during deep drawing of sheet.

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위

본문
키워드

머릿글
요약

이 문서는 전체 문서 중 일부분입니다. 이 주제에 대해 더 읽고 싶으시면 아래 링크를 클릭하시면 됩니다.

Total Materia는 다양한 나라와 규격에 따른 수천개의 알루미늄 재질에 대한 정보를 포함하고 있습니다.

재질의 화학적 조성, 기계적 특성, 물리적 특성, 고급 물성 데이터 등의 전체적인 특성 정보들을 어디서든 검토하실 수 있습니다.

고급 검색을 이용하여, 검색 조건의 재질 리스트에서 '알루미늄'을 선택합니다. 검색 범위 좀 더 줄이기를 원하신다면 국가/규격과 같은 다른 조건을 지정할 수 있습니다.

검색 버튼을 클릭합니다.


선택된 정보에 부합하는 일련의 재질이 검색됩니다.


결과 리스트에서 재질을 선택하시면, 일련의 규격 사양 소그룹이 나타납니다.

여기에서 선택한 재질의 특정 특성 데이터를 검토하실 수도 있고, 강력한 상호 참조 표를 이용하여 유사 재질이나 등가 재질을 검토하는 것 또한 가능합니다.


자세한 특성 데이터를 보시려면 특성 데이터 링크를 클릭하세요.




Total Materia 데이터베이스를 사용해 보실 수 있는 기회가 있습니다. 저희는 Total Materia 무료 체험을 통해 150,000명 이상의 사용자가 이용하고 있는 커뮤니티로 귀하를 초대합니다.