Retrogression and Re-aging Heat Treatment: AA7XXX Aluminum Alloys

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.

Characterization of AMAG AL6-CHA Sheet Material for Chassis Application in the Automotive Industry

Aluminium is already extensively used in car production to reduce the CO2 emissions by weight reduction. A further beneficial effect of lightweight design can be generated in components of the chassis by reducing the weight of unsprung mass thereby enhancing the driving comfort and reducing the noise level. The medium strength alloys of the type AlMg3Mn (EN AW-5754) and AlMg3.5Mn (EN AW-5454) are currently the aluminium sheet material choice for application in chassis components. The newly developed alloy AMAG AL6-CHA was optimized with regard to chassis applications and shows the potential of significant increase of the mechanical properties compared to state-of-the-art 5xxx series alloys. AMAG AL6-CHA, which is a 6xxx series alloy with balanced Mg/Si-ratio, is characterized with regard to mechanical properties and intergranular corrosion resistance in delivery temper T4 and after artificial aging with the typical heat treatment cycle 205 °C/60 min in peak aged temper T6. Furthermore we will show the results of the Charpy-V-notch impact test and the formability is described per bend test and grain size analysis.

Ageing of Brazed Aluminium AA6xxx Alloys for Vehicle Radiators

Some aluminium alloys with Mg-Si age-hardening are used in vehicle radiators. For cost reasons they are preferably delivered in a naturally aged temper. Estimated minimum time of natural ageing between brazing and when the radiator is taken into service is 14 days. At the service temperature of 95°C, the radiator material will continue to age harden. For accelerated durability testing it is vital to use a radiator with the strength and ageing response of a service radiator. We investigated whether the full 14 days of natural ageing were needed, or if the time could be shortened. Since a vehicle is not in constant use, the radiator temperature will vary over time. We therefore compared cyclic ageing between ambient temperature and 95°C to continuous ageing at 95°C. The Sapa Heat Transfer alloys FA7870 (for headers) and FA7850 (for tubes) were subjected to different ageing times at different temperatures. Tensile and hardness were performed to assess the ageing effect. It was found that natural ageing reduced hardening during the subsequent ageing at service temperature ageing effect, an effect that was most pronounced for the first four days. There was no difference between continuous and cyclic ageing.

Investigation on Microstructure and Corrosion Behaviour of 6XXX Series Aluminium Alloys

Microstructure and corrosion behaviour of 6061 and 6013 sheet material were investigated in the naturally aged and peak-aged heat treatment conditions. Transmission electron microscopy did not reveal strengthening phases in the naturally aged sheet. In the peak-aged temper, β’’ precipitates were observed in alloy 6061, whereas both β’’ and Q’ phases were present in 6013- T6 sheet. Marked grain boundary precipitation was not found. Corrosion potentials of the alloys 6061 and 6013 shifted to more active values with increasing aging. For the copper containing 6013 sheet, the potential difference between the tempers T4 and T6 was more pronounced. When immersed in an aqueous chloride-peroxide solution, alloy 6061 suffered predominantly intergranular corrosion and pitting in the tempers T4 and T6, respectively. On the contrary, 6013 sheet was sensitive to pitting in the naturally aged condition, and intergranular corrosion was the prevailing attack in the peak-aged material. Both alloys 6061 and 6013 were resistant to stress corrosion cracking in the tempers T4 and T6.

Damage Tolerance Capability of an Al-Cu-Mg-Ag Alloy (2139)

The effects of dispersoid forming elements on the mechanical properties of Al-Cu- Mg-Ag alloys are examined. It is found that a small amount of Zr addition is detrimental to the damage tolerance of Al-Cu-Mg-Ag alloys in artificially aged temper, while Mn addition is beneficial. The superior damage tolerance capability of Alloy 2139 is demonstrated by comparing it to other high performance alloys used for DT critical applications

SANDVIK NANOFLEX

Sandvik Nanoflex is a corrosion-resistant precipitation-hardening austenitic stainless steel that is both formable in the received condition and strong in the aged temper. This datasheet provides information on composition, physical properties, and tensile properties as well as fatigue. It also includes information on corrosion resistance as well as forming, heat treating, and joining. Filing Code: SS-956. Producer or source: Sandvik Steel Company.