Age Hardening of Aluminum Alloys

Abstract

This article describes the effects of alloying and heat treatment on the metastable transition precipitates that occur in age hardenable aluminum alloys. Early precipitation stages are less well understood than later ones. This article details the aging sequence and characteristics of precipitates that occur in the natural aging and artificial aging of Al-Mg-Si-(Cu) alloys, Al-Mg-Cu alloys, microalloyed Al-Mg-Cu-(Ag, Si) alloys, aluminum-lithium-base alloys, and Al-Zn-Mg-(Cu) alloys. Crystal structure, composition, dimensions, and aging conditions of precipitates are detailed. Effects of reversion, duplex annealing, and retrogression and re-aging are included.

On the Role of Microstructure and Defects in the Room and High-Temperature Tensile Behavior of the PBF-LB A357 (AlSi7Mg) Alloy in As-Built and Peak-Aged Conditions

“…A soaking time of 30 min was adopted for high-temperature tests to homogenize the sample temperature before the test. The temperature of 200 °C was chosen based on the service life of power-train components and on the threshold temperature at which microstructural coarsening of conventional cast alloys occurs [ 3 , 4 ].…”

“…However, for these specific applications, it is crucial to guarantee a high strength at elevated temperatures (up to 200–250 °C) that engine components can commonly experience during their service life [ 3 ]. Conventional cast A356 or A357 T6 alloys suffer a non-negligible decrease in mechanical strength if exposed to temperatures close to 200 °C due to coarsening of reinforcing phases related to over-aging [ 4 ]. For high-temperature applications, alloys containing a certain amount of Cu assure better thermal stability [ 4 , 5 ].…”

“…Conventional cast A356 or A357 T6 alloys suffer a non-negligible decrease in mechanical strength if exposed to temperatures close to 200 °C due to coarsening of reinforcing phases related to over-aging [ 4 ]. For high-temperature applications, alloys containing a certain amount of Cu assure better thermal stability [ 4 , 5 ]. However, the effect of thermal exposure on the microstructure and mechanical properties of AlSi7Mg alloys processed by innovative additive manufacturing technologies, like laser-based powder bed fusion (PBF-LB), is currently lacking.…”

Coaxial Wire Laser-based Additive Manufacturing of AA7075 with TiC Nanoparticles

“…As aging continues for a few hours, GP zones grow to a size where intermediate phase η' can precipitate, which is semi-coherent and is the main hardening phase in AA7075 [15,16]. Furthermore, since Mg content in AA7075 is rather high, an intermediate phase T' can nucleate directly from the supersaturated solid solution, forming a semi-coherent precipitate that can contribute to hardness increase [17]. Finally, after approximately 24 hours of aging the growth and coarsening of η' results in the formation of the equilibrium phase η, with composition Mg(Zn,Cu,Al)2.…”

“…This phase is incoherent and therefore, as its content increases the mechanical strength of the alloy is reduced, e.g. over-aging occurs [15,17].…”