Improved corrosion resistance and mechanical properties of severely deformed ZM31 alloy.

The hexagonal close-packed (HCP) crystal structure of Mg alloys lead to poor formability as well as other undesirable mechanical behaviors in an otherwise highly sought-after alloy for commercial use. This study investigates the evolution of microstructure, texture, corrosion and mechanical behaviors in Mg-Zn-Mn (ZM31) alloy after processing using Equal Channel Angular Pressing (ECAP). Dynamic recrystallization was evident in the ECAP-processed samples, correlated with a substantial fiber structure, and resulted in the attainment of notable grain refinement and high lattice strain. Average grain sizes of 2.2 and 2 µm were achieved via 2 and 4-Pass Bc processing, respectively. This significant refinement yielded lower corrosion rates through enhancement of the thickness, coherency, and stability of formed protective oxide layers. The corrosion rate in the NaCl medium was substantially enhanced by 99.5% after four passes via route Bc. The recrystallized fine structure was found to have contributed to yield strength, ultimate strength, and microhardness improvements. Deformation enhanced yield and ultimate strengths by 132% and 64%, respectively. The distinctive grain refinement mechanism exhibited through the current ECAP procedure has potential to pave the way for novel and impactful utilizations of ZM31 in industries that demand exceptional mechanical and corrosion performance.

Effect of Aging Treatment on the Strength and Microstructure of 7075-Based Alloys Containing 2% Li and/or 0.12% Sc.

The present study was performed on three versions of 7075 alloy to which Sc or Sc + Li was added. The alloys were subjected to various aging treatments. The microhardness results show that the highest value of hardness was achieved when the alloy containing Li + Sc was aged at 120 °C for 24 h whereas the minimum level was exhibited by the base alloy aged at 280 °C. The results were interpreted in terms of the size and distribution of the main hardening phase (η'(MgZn2)), and the role of the presence of Al and Cu in the used alloy. Precipitation of Al3(Sc, Zr, Ti) phase particles during solidification of the Sc-containing ingots was also discussed. The coarsening and spheroidi-zation of η-phase particles take place through the Ostwald ripening mechanism while smaller par-ticles in solution dissolve and deposit on larger particles. In Sc-containing alloys, star phase particle consists of different layers. The change in the brightness from layer to layer indicates that the Zr and Sc concentrations are varied within the star phase, since the atomic number of Zr (40) is higher than the atomic number of Sc (21). The addition of Sc, as well, leads to marked decrease in the grain size of the as-cast alloys i.e., 300 µm and 45 µm, respectively. The interaction between Li and Sc would reduce the effectiveness of the grain refining effect of Sc. The results of the refining effect of Sc were confirmed using the EBSD technique.

Investigating the Effect of Heat Treatment on the Microstructure and Hardness of Aluminum-Lithium Alloys.

In this study, the effects of heat treatment on the microstructure and strength (micro-hardness) of an aluminum-lithium (Al-Li) base alloy containing copper (Cu) and scandium (Sc) were investigated, with a view to enhancing the alloy performance for aerospace applications. The heat treatment conditions were investigated to understand the precipitation behavior and the mechanisms involved in strengthening. Aging was carried out at temperatures of 130 °C and 150 °C for aging times of 1 h, 2.5 h, 5 h, 10 h, 15 h, 25 h, 35 h, and 45 h at each temperature for Al-Li alloy and at 160 °C, 180 °C, and 200 °C for aging times of 5 h, 10 h, 15 h, 20 h, 25 h, and 30 h at each temperature for Al-Li-Cu and Al-Li-Cu-Sc alloys. The investigation revealed that both solution heat treatment and artificial aging had a notable impact on strengthening the hardness of the alloy. This effect was attributed to the characteristics of the precipitates, including their type, size, number density, and distribution. The addition of copper (Cu) and scandium (Sc) was observed to have an impact on grain size refinement, while Cu addition specifically affected the precipitation behavior of the alloy. It led to remarkable changes in the number density, size, and distribution of T1 (Al2CuLi) and θ' (Al2Cu) phases. As a result, the hardness of the alloy was significantly improved after the addition of Cu and Sc, in comparison with the base Al-Li alloy. The best heat treatment process was determined as: 580 °C/1 h solution treatment +150 °C/45 h artificial aging for Al-Li alloy and 505 °C/5 h solution treatment +180 °C/20 h artificial aging for Al-Li-Cu and Al-Li-Cu-Sc alloys.

The Role of Mg Content and Aging Treatment on the Tensile and Fatigue Properties of Die-Cast 380 Alloy.

The main objective of this contribution was to determine the impact of magnesium (Mg) concentration and solidification rate (about 800 °C/s) on the mechanical properties of commercial A380.1 die-cast alloy. Respective amounts of 0.10%, 0.30%, and 0.50% Mg were used to establish their influence on the main tensile properties, namely, the ultimate limit, the elastic limit, and the percentage of elongation to fracture. The study also focused on the effect of magnesium on the fatigue behavior of A380.1 alloy where the role of surface defects and internal defects (porosity, oxide films, and inclusions) on the alloy fatigue life was also determined. The tensile properties were analyzed in order to optimize the heat treatments of T6 (under-aging) and T7 (over-aging). Consequently, the influence of several parameters was evaluated using tensile testing and optical and scanning electron micrography. Fatigue strength was investigated by performing rotational bending tests. The results show that the alloy tensile strength parameters improve with up to 0.3% Mg. Further addition of Mg, i.e., 0.5%, does not produce any significant improvement with respect to either traction or fatigue. It is observed that the tensile properties fluctuate according to the Guinier-Preston zones which occur during heat treatment, while the fatigue properties decrease as the Mg content increases. In contrast to a mechanical fatigue failure mechanism, in the present study, cracks were initiated at the sample's outer surface and then propagated toward the center.

Assessment of the Influence of Additives on the Mechanical Properties and Machinability of Al-11%Si Cast Alloys: Application of DOE and ANOVA Methods.

In the present study, the statistical design of experiments (DOE) method was applied to study and control the properties of near-eutectic Al-11%Si alloys. In this study, we developed regression equations between response variables, including hardness, yield stress, ultimate tensile stress, elongation, total cutting force, cutting power, and tool life, and varying factors which included the percentage of the alloying element in the composition and the modification level. These equations may be analyzed quantitatively to acquire an understating of the effects of the main variables and their interactions on the mechanical behavior and the machinability of the alloy under investigation. Analysis of variance (ANOVA) was performed to verify the fit and adequacy of the developed mathematical models. The results show that increasing the levels of Cu and Fe results in an increase in hardness, yield stress and ultimate tensile strength in both modified and non-modified alloys. On the other hand, both Cu and Fe appear to affect the elongation adversely, whereas the Sr level shows a positive effect on the elongation percentage. We found that the Sr level had the most significant effect on the cutting forces and cutting power, followed by Fe and Cu contents.

Intermetallics Formation during Solidification of Al-Si-Cu-Mg Cast Alloys.

The present study was undertaken to examine the effect of iron, manganese, copper and magnesium on the microstructural characteristics of Al-11%Si-2%Cu-Mg-based alloy referred to as 396 under different working conditions. The results show that strontium (Sr) has high affinity to react with magnesium (Mg), resulting in reduced effectiveness as eutectic silicon modifier or age hardening agent. In addition, Sr alters the sequence of the precipitation of the α-AlFeMnSi phase from post-eutectic to pro-eutectic which would harden the soft α-Aluminum matrix. The mechanism is still under investigation. The interactions between iron (Fe) and Mg and Sr-Mg result in the formation of serval dissolvable intermetallics during the solutionizing treatment such as ß-AlFeSi, π-AlFeMgSi and Q-AlMgSiCu phases. The study also emphasizes the role of modification and grain refining as well as intermetallics in porosity formation and hardness of samples aged in the temperature range 155-240 °C.

Effect of Intermetallics and Drill Materials on the Machinability of Al-Si Cast Alloys.

The present study was conducted on the machinability of 396 alloy (containing approximately 11% Si) and B319.2 alloy mainly to emphasize the effects of Fe-intermetallics, i.e., α-Fe, ß-Fe, and sludge. The results demonstrate that the presence of sludge in the form of hard spots has a significant effect on cutting forces and tool life, in that it decreases drill life by 50% compared to the base alloy. The formation of the α-Fe phase in the M1 base alloy has a beneficial effect on tool life in that this alloy produces the highest number of holes drilled compared to alloys containing sludge or ß-Fe; this result may be explained by the fact that the formation of the α-Fe intermetallic, with its rounded Chinese script morphology and its presence within α-Al dendrites, is expected to improve matrix homogeneity via hardening of the soft α-Al dendrites. Increasing the Fe-content from 0.5% to 1% in the 396-T6 alloy containing 0.5% Mn produces a distinct improvement in alloy machinability in terms of cutting force and tool life. The addition of Fe and/or Mn appears to have no discernible effect on the build-up edge area (BUE) and chip shape.

Effects of Trace Elements on the Microstructural and Machinability Characteristics of Al-Si-Cu-Mg Castings.

This study was undertaken to emphasize the influence of Sn and Bi addition on the machinability of Sr-modified, grain-refined, and heat-treated Al-Si B319 and 396 alloys. Drilling and tapping tests were conducted to examine the cutting forces, tool life, tool wear, built-up edge evolution, and chip shape. Microstructures were examined using optical and electron microscopy. Drilling test results show that the B319.2 alloy with 0.15%Sn yields the longest drill life, i.e., twice that of the B319.2 alloy containing 0.5%Bi, and one-and-a-half times that of the B319.2 alloy containing 0.15%Sn + 0.5%Bi. The presence of 0.5%Bi in the B319.2 alloy causes a deterioration of drill life (cf., 1101 holes with 2100 holes drilled in the B319.2 alloy containing 0.15%Sn). The α-Fe phase in the 396 alloy produces the highest number of holes drilled compared with alloys containing sludge or ß-Fe. The presence of sludge decreases the drill life by 50%. Built-up edge (BUE) measurements and optical photographs show little change in the BUE width for different numbers of holes except for the B319.2 alloy containing 0.5%Bi, which shows a slightly lower width (0.166 mm) compared with that containing 0.15% Sn (0.184 mm) or 0.15%Sn + 0.5%Bi (0.170 mm).