Influence of Intensive Melt Shearing on the Microstructure and Mechanical Properties of an Al-Mg Alloy with High Added Impurity Content

Abstract

We have investigated the influence of melt conditioning by intensive shearing on the mechanical behavior and microstructure of Al-Mg-Mn-Fe-Cu-Si alloy sheet produced from a small book mold ingot with high added impurity content. The melt conditioned ingot has fine grains throughout its cross section, whereas a conventionally cast ingot, without melt shearing, has coarser grains and shows a wider variation of grain size. Both needle-shaped and coarse Chinese script iron bearing intermetallic particles are found in the microstructure at the center of the conventionally processed ingot, but for the melt conditioned ingot, only fine Chinese script intermetallic particles are observed. In addition to the iron bearing intermetallics, Mg 2 Si particles are also observed. The ingots were rolled to thin sheet and solution heat treated (SHT). During rolling, the iron-based intermetallics and Mg 2 Si particles are broken and aligned along the rolling direction. Yield strength (YS), ultimate tensile strength (UTS), and elongation of the intensively melt sheared and processed sheet are all improved compared to the conventionally cast and processed sheet. Fractographic analysis of the tensile fracture surfaces shows that the clustered and coarse iron bearing intermetallic particles are responsible for the observed reduction in mechanical properties of the conventionally cast sheet. We have shown that by refining the initial microstructure of the ingot by intensive shear melt conditioning, it is possible to achieve improved mechanical properties at the final sheet gage of an AlMgMn alloy with a high content of impurities.

Evolution of Fe Bearing Intermetallics During DC Casting and Homogenization of an Al-Mg-Si Al Alloy

“…Although the SEM investigations revealed discrete Si particles (Figure 12(b)), the absence of Si in XRD analysis was probably because the volume fraction was too low for detection. It should also be noted that by comparison with previous work in, [18] the present work suggests that thermodynamic predictions of phase fractions only indicate formation of b-AlFeSi, consistent with experiment, when non-equilibrium (no solid diffusion) assumptions were used.…”

“…So long as the b to a c AlFeSi transformation is completed, finer intermetallic particles in the billet before downstream deformation process will improve both the deformation efficiency and final property of the product. [15,18] …”

“…Among the factors that govern the homogenization response, the initial cast microstructure and the alloy chemical composition play key roles. Therefore, in developing new solidification processing routes [15] or advanced solidification technologies [17][18][19][20] that seek to promote more favorable as-cast microstructures, it is important to understand better the link between microstructural evolution in casting and the subsequent homogenization response of the secondary phases. For example the cooling rate and solid/liquid growth velocity in DC casting significantly affect the proportions of a c -AlFeSi and b-AlFeSi in the final microstructure.…”

Influence of Al grain structure on Fe bearing intermetallics during DC casting of an Al-Mg-Si alloy

“…Thus for the first time, we have systematically studied these individual effects on near industrial scale DC cast billets. This study will therefore be useful for industry to optimize their existing casting practice and to develop advanced solidification casting technologies [10,[25][26][27][28][29][30][31][32] e.g. to produce billet (using complex alloys from recycled materials) with more favourable microstructures for better downstream processing yielding good quality end products.…”

Structure Property Correlation of Al Based MMC Reinforced with Cu Coated Rice Husk Ash SiO2 Particles

“…It is assumed that the Si comes mainly from the reaction of the SiO 2 with Al-Mg matrix. A reaction between Mg and SiO 2 leads to Mg 2 Si, MgAl 2 O 4 and MgO [17,18]. As a result, SiO 2 particles were observed to get consumed in the spinel formation such as Mg 2 Si, MgAl 2 O 4 and other intermetallic phase viz.…”