Evaluation of Age Hardening Behavior Using Composite Rule and Microstructure Observation in Al-Si-Mg Alloy Castings

Abstract

Al-Si hypoeutectic alloys have excellent castability and sufficient strength in combination with other alloying elements. Especially, Al-Si alloy containing Mg used for high-quality die-casting is well-known as a high strength alloy brought by the appropriate heat treatment and consequential precipitation hardening of Mg 2 Si intermediate phase. T6-heat treatment must be applied for maximum strength, but solution at high temperature and quenching treatment often conduct the product deformation and extra cost for fabrication. Therefore only artificial aging (T5-heat treatment) at comparatively lower temperature is mainly applied to industrial die-casting products. However, there are few studies on age hardening characteristics supplied by T5-heat treatment to Al-Si hypoeutectic alloys. To understand the age hardening behavior of Al-10 mass%Si-0.5 mass%Mg and Al-10 mass%Si-0.8 mass%Mg alloys in detail, microstructure observation and hardness measurement were performed. These alloys quenched in iced water, naturally aged at room temperature and artificially aged at 423-523 K, showed conspicuously age hardening behavior. Age hardening of Al-Si-Mg alloy generally considered to be the main cause of the precipitation-based hardening in phase, nevertheless it was seen that precipitation occurred in -Al+Si eutectic phase. Consequently, from the microstructure observation using SEM, it's thought that the age hardening of these alloys was mainly composed of the hardness change in -Al+Si eutectic phase.

Precise analysis of effects of aging on mechanical properties of cast ADC12 aluminum alloy

“…At aging temperatures of 433, 448 and 463 K, the hardness increases remarkably during the early stage of aging, and aging peaks in hardness variation are obtained when samples are heated for 10-15 h. At an aging temperature of 448 K, a clear aging peak with the highest hardness is detected at about 13 h, where strong precipitation hardening would have occurred. A similar result was observed in the previous work by Sjölander and Seifeddine [9], where Al-7Si-0.45Mg-xCu (0-3%) alloys were aged at 448 K and high hardness values were detected at about 10 h. Another approach was adopted by Furui et al [5], using Al-Si10-Mg0.5 alloy, in which high hardness was obtained at an aging temperature of 423 K, but low hardness at 473 and 523 K. It is interesting to note that the hardness variations for the samples aged at 433, 448 and 463 K seem to have double aging peaks. Similar double aging peaks were identified by Li et al [11], who investigated the age-hardening behavior of cast Al-Si 9.55 -Cu 1.48 -Mg 0.53 alloys (in wt%).…”

“…With the aim of obtaining excellent mechanical properties for cast aluminum alloys, heat treatment was carried out under a number of aging conditions, with the aging temperature and time determined on the basis of previous work [3,5,11]. The aging process was conducted to and held at five different temperatures (418, 433, 448, 463 and 493 K) and the aging time ranged from 1 to 200 h. Before the aging process, solution treatment was carried out, in which the samples were heated to 773 K for 10 h in an air furnace followed by water quenching.…”

“…Although some researchers have investigated age-hardening characteristics with the aim of obtaining high mechanical properties for aluminum alloys [5,11,12], the associated experimental data are not sufficient to allow determination of suitable aging conditions. This is because, in previous studies, the heat treatments were conducted at only a few aging temperatures and for small number of aging times.…”

“…A highstrength alloy suitable for high-quality die-casting has been produced from Al-Si alloy containing Cu and Mg by appropriate heat treatment with resulting precipitation hardening of Al 2 Cu and Mg 2 Si intermediate phases [4,5]. The precipitation sequence during the aging of aluminum alloys goes through several intermediate stages before the formation of equilibrium precipitates.…”

Microstructural, mechanical and electrical characterization of directionally solidified Al–Si–Mg eutectic alloy

“…solid solution, precipitation, grain size refinement, dispersion, work hardening and fiber reinforcement [9]. Al-Mg-Si alloys are being increasingly used in automotive and aerospace industries for critical structure applications because of their excellent castability, corrosion resistance and good mechanical properties in the heat treated conditions and consequential precipitation hardening of Mg 2 Si intermediate phase [10][11][12][13]8].…”