Influence of Heat Treatment Upon Microstructure of Casting Aluminum Alloys

The effects of equal channel angular pressing (ECAP), further heat treatment and rolling on the structure and room temperature mechanical properties of the commercial aluminum alloys 6061 (Al-0.9Mg-0.7Si) and 1560 (Al-6.5Mg-0.6Mn) were investigated. It has been shown that the strength of the alloys after ECAP is higher than that achieved after conventional processing. Prior ECAP solution treatment and post-ECAP ageing can additionally increase the strength of the 6061 alloy. Under optimal ageing conditions a yield strength (YS) of 434 MPa and am ultimate tensile strength (UTS) of 470 MPa were obtained for the alloy. Additional cold rolling leads to a YS and UTS of 475 and 500 MPa with 8% elongation. It was found that the post-ECAP isothermal rolling of the 1560 alloy resulted in the formation of a nano-fibred structure and a tensile strength (YS = 540 MPa and UTS = 635 MPa) that has never previously been observed in commercial non-heat treatable alloys.

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Uphill Quenching of Aluminum Alloys

Encyclopedia of Aluminum and Its Alloys ◽

10.1201/9781351045636-140000235 ◽

2019 ◽

Author(s):

Wellington da Silva Mattos ◽

George Edward Totten ◽

Lauralice de Campos Franceschini Canale

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Residual Stress ◽

Aluminum Alloys ◽

Temperature Gradient ◽

Dimensional Stability ◽

Steam Chamber ◽

Conventional Heat Treatment ◽

Quenching Process ◽

Uphill Quenching

This article describes the concept of uphill quenching process applied in the heat treatment of aluminum alloys. Uphill quenching is interesting since residual stress reductions of up to 80% has been reported. In addition, substantial improvements in dimensional stability have been achieved for several types of aluminum parts. Often, uphill quenching is applied after quenching and before aging during the heat treatment of aluminum alloys. The uphill quenching process consists of the immersion of the part in a cryogenic environment, and after homogenization of the temperature, the part is transferred to the hot steam chamber to obtain a temperature gradient that will maintain the mechanical properties gained with this process. The results obtained are lower residual stress and better dimensional stability. The aim of this article is to provide a review of this process and to compare it with conventional heat treatment.

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Retrogression and Re-aging Heat Treatment: AA7XXX Aluminum Alloys

Encyclopedia of Aluminum and Its Alloys ◽

10.1201/9781351045636-140000213 ◽

2019 ◽

Author(s):

V. Anil Kumar ◽

S. Arjun ◽

R.K. Gupta ◽

P.V. Venkitakrishnan

Keyword(s):

Heat Treatment ◽

Aluminum Alloys ◽

Industrial Applications ◽

Age Hardening ◽

Large Cross Section ◽

Structural Applications ◽

The Matrix ◽

Peak Aged ◽

Aged Temper ◽

Short Time

Retrogression and re-aging (RRA) treatment was introduced to increase the stress corrosion cracking (SCC) resistance while retaining the strength attainable in T6 (peak aged) temper. Retrogression is a short-term heat treatment at an elevated temperature wherein a partial dissolution of metastable precipitates occurs, which are responsible for the hardening. During the next step, the material is re-aged in the regime of typical age hardening parameters to restore the strength with improved ductility. Response of RRA treatment has been reported on AA7XXX series Aluminum alloys such as AA7075, AA7050, AA7150, AA7049, and AA7010. Studies have been done on the effect of RRA on microstructure, mechanical properties such as tensile and hardness, corrosion, exfoliation corrosion, and SCC resistance by various researchers. The key characteristic of RRA is retrogression, which makes the re-precipitation in the matrix and coarsening of grain boundary precipitates such as MgZn2, η′. The retrogression treatment however requires high temperature and a short time, which limits the industrial application of RRA, especially in the heat treatment of the components with large cross section, due to the inherent thermal conductivity limitations. Hence, further work needs to be done in this area to apply this specialized heat treatment for industrial applications. This article brings out a comprehension of the changes in microstructure, tensile properties, and corrosion resistance of the various commonly used AA7XXX Aluminum alloys in structural applications with RRA heat treatment. The future scope of the work in RRA heat treatment is also discussed in this article.

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