The clustering behavior during natural aging (NA) and subsequent artificial aging (AA) at 170°C in Al–Mg–Si alloys with the different Mg/Si ratio is evaluated using three-dimensional atom probe (3DAP). The internal composition of clusters formed during short-term NA is strongly associated with the alloy composition and prolonged NA leads to the formation of clusters with a Mg : Si ratio close to 1. The number density of clusters decreases with no dependence on the cluster size, and Si-rich clusters with Mg/(Mg+Si) values inside clusters below 0.4 show little variation during AA for 1.2 ks. It is believed that Mg–Si clusters with ranging from 0.4 to 0.6 in the Mg/(Mg+Si) value inside clusters can both dissolve and grow during AA. It is revealed that the delay in age hardening in the early stage of AA is closely related to the number density of the Si-rich and Mg–Si clusters.
The microstructural evolution and changes in mechanical properties of 6000 series aluminum alloys during multi-directional forging (MDFing) and artificial aging were systematically investigated. The strength gradually increased with increasing cumulative strain. The MDFed sample up to a cumulative strain of ΣΔε=6 showed the yield strength of 252 MPa and the ultimate tensile strength of 282 MPa. MDFing evolved unique deformation texture at higher cumulative strain region. Artificial aging at 373 K and 393 K after MDFing caused moderate hardening, although softening took place over 423 K without any obvious hardening. The artificially aged sample at 393 K for 100 ks after MDFing exhibited well-balanced mechanical properties of 288 MPa yield strength and 313 MPa ultimate tensile strength with 18.9% plastic strain to failure. The MDFing and subsequent aging succesfully produced homogeneous ultrafine-grained structure with average (sub)grain size of 220 nm.
At present, the strength of most of Al–Mg–Si alloy bolts is not enough, and thus highly expected to be increased, for example, to >500 MPa in ultimate tensile strength (UTS). In this study, mechanical strength of A6056 Al–Mg–Si alloy was aimed at improving, without diminishing the elongation, by combined application of equal-channel angular pressing (ECAP) and various aging treatments. Multi-pass ECAP and pre-aging (PA) treatment at 373 K for 1.2 ks was found to be effective in strengthening the bolt material subject to room-temperature storage followed by artificial aging. Especially, PA plus ECAP 2pass treatment exerted the biggest impact on the strength (i.e., 514 MPa in UTS) with a reasonable elongation to fracture (i.e., 16%). Such a high strength and good ductility exceeds minimum requirement for aluminum-made bolts registered in JIS B1057, and thus the developed PA-ECAP 2pass specimen can be utilized potentially as a high-strength bolt material.
In the present study, we have examined the compression response of single-crystal cylindrical micropillars with different diameters (approximately ranging from 1 to 10 µm) and shape parameters prepared on the sample surface of 4N purity aluminum (Al) sheets with the recrystallized microstructure. The compression tests for micropillars with various sizes demonstrated the flow stress of micropillars increases with decreasing pillar diameter. The observed size dependence of resolved shear stress for slip corresponds well to the previous studies on micropillars prepared from 3N and 5N purity Al sheets. The measured shear stress resolved onto a primary slip system (τi) scaled by shear modulus (G) and the pillar diameter (d) scaled by Burgers vector (b) shows the following correlation: (τi/G)=0.33(d/b)−0.63. The compression response of micropillars with different d1/d2 (ratio of top diameter (d1) to bottom diameter (d2) of cylindrical micropillars) revealed higher d1/d2 than 0.5 is required for precisely measuring the strength of cylindrical micropillars, which was confirmed by the observations of compressed micropillars.
Corrosion mechanism and morphology changes of aluminum alloy in model solution corresponding sea water containing gluconates and zinc ions were investigated by immersion corrosion tests with surface analysis. Surface and cross-sectional SEM results showed that zinc ions suppress the morphology changes of aluminum alloy in the solution containing gluconates. XPS analyses indicated that gluconates in the solutions adsorb on the oxide films of aluminum alloy and protective films of the adsorbed gluconates would prevent the penetration of chloride ions to the aluminum alloy. The XPS results also suggest that zinc ions in the solutions bond to the oxide film of aluminum alloy and zinc ions enhance the corrosion inhibition ability of the protective films of gluconates for aluminum alloy in model sea water.