Effect of Cooling Rate on the Microstructure Evolution and Mechanical Properties of Iron-Rich Al–Si Alloy

The mechanical properties of iron-rich Al–Si alloy is limited by the existence of plenty of the iron-rich phase (β-Al5FeSi), whose unfavorable morphology not only splits the matrix but also causes both stress concentration and interface mismatch with the Al matrix. The effect of the cooling rate on the tensile properties of Fe-rich Al–Si alloy was studied by the melt spinning method at different rotating speeds. At the traditional casting cooling rate of ~10 K/s, the size of the needle-like β-Al5FeSi phase is about 80 μm. In contrast, the size of the β-Al5FeSi phase is reduced to 500 nm and the morphology changes to a granular morphology with the high cooling rate of ~104 K/s. With the increase of the cooling rate, the morphology of the β-Al5FeSi phase is optimized, meanwhile the tensile properties of Fe-rich Al–Si alloy are greatly improved. The improved tensile properties of the Fe-rich Al-Si alloy is attributed to the combination of Fe-rich reinforced particles and the granular silicon phase provided by the high cooling rate of the melt spinning method.

Microstructure and Mechanical Property of Al6Si2Cu Alloy Subjected to Double-Solution Heat Treatment

This study aims to develop the mechanical properties of the Al6Si2Cu aluminum alloy through the double-solution treatment. In addition to the Al matrix, large amounts of coarse eutectic Si, Al2Cu intermetallic, and Fe-rich phases were generated through thermo-calc simulation in agreement with the equilibrium phases. The eutectic Si phase is fragmented and spheroidized by the solution treatment as the heat treatment temperature and time increase. The Al2Cu intermetallic phase is dissolved into the Al matrix, resulting in an increase in both strength and elongation. The second-step solution temperature at 525 °C should be an optimum condition for enhancing the mechanical properties of the Al6Si2Cu aluminum alloy.

Comparative Study on the Corrosion Resistance of 6061Al and SiC3D/6061Al Composite in a Chloride Environment

Interface problems and the destruction of the continuity of the oxide film in the Al matrix usually reduce the corrosion resistance of the material. In this paper, the corrosion resistance of Al matrix composites (AMCs) was improved by introducing the silicon carbide skeletons (SiC3D) obtained with polymer replica technology. SiC3D/6061Al was fabricated by infiltrating molten 6061Al alloy in the oxidized SiC3D using the low-pressure casting method. The corrosion resistance performances of 6061Al and SiC3D/6061Al in NaCl solution were studied by electrochemical, neutral salt spray corrosion (NSS), and salt leaching (SL) tests. Results show corrosion resistance of SiC3D/6061Al is higher than that of 6061Al alloys by open circuit potential (OCP), potentio-dynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. However, NSS and SL tests show the corrosion resistance of SiC3D/6061Al is lower than that of 6061Al alloy. The reason is a corrosion resistant and anti-oxidation network macrostructure with large interface recombination, few concentrated interfaces, and a small specific area that formed in SiC3D/6061Al. SiC3D cannot damage the continuity of the Al2O3 passivating film, and the network macrostructure greatly improves the corrosion resistance performance.

Effect of Rod-like Structure on Fatigue Life, Short Surface Crack Initiation and Growth Characteristics of Extruded Aluminum Alloy A2024 (Analysis via Modified Linear Elastic Fracture Mechanics)

In the Al alloy A2024-T3 extruded material, a rod-like structure is generated parallel to the extrusion direction. In this study, the effects of rod-like structures on fatigue crack initiation and growth behavior were comprehensively investigated. Two types of specimens were used in a fatigue experiment, in which the direction of the load stress amplitude was parallel (specimen P) and perpendicular (specimen V) to the rod-like structure. Based on the experimental and analytical results, the following findings were obtained regarding the fatigue life, location of crack initiation, and fatigue crack growth behavior. Because the fatigue life of specimen P was longer than that of specimen V, it is inferred that the rod-like structure significantly affects the fatigue life. In specimen P, fatigue cracks were generated from the grain boundaries of the Al matrix. By contrast, in specimen V, cracks were generated from the Cu–Mg-based intermetallic compound in the Al matrix. In specimen P, fatigue cracks were more likely to propagate across the rod-like structure, which decreased the fatigue crack growth rate. In specimen V, fatigue cracks did not propagate across the rod-like structure; instead, they propagated through the Al matrix. Therefore, the fatigue crack growth resistance of specimen V was lower than that of specimen P. The relationship between the fatigue crack growth rate and the modified linear elastic fracture mechanics parameter could be used to predict the S–N curve (stress amplitude vs. fatigue life) and fatigue crack growth behavior. The predicted results agreed well with the experimental results.

Effect of the Hot Deformation Conditions on Structure and Mechanical Properties of AlCr/AlCrSi Powder Composites

Aluminum matrix composites usually contain strengthening particles of refractory compounds (SiC, Al2O3) that do not react with the Al matrix. There is a problem in producing the Al matrix composite with inclusion of metals that can generate intermetallic compounds with aluminum. In this case, a conventional sintering of powder mixtures results in high porosity due to volume growth. That is why some new methods of producing dense Al matrix composites are required. A possibility to create a dense powder Al-based composite containing hard components, such as chromium and silicon, without using the sintering process, is considered. This paper presents study results of structural and mechanical properties of Al-Cr and Al-Cr-Si composites produced by hot compaction of powder mixtures. An analysis of the relationship between mechanical properties and structures of Al-Cr and Al-Cr-Si composites is carried out. Optimal values for thermomechanical processing modes that ensure sufficient strength and plasticity are determined. It is shown that strong bonding of the aluminum particles occurs under hot deformation, and an aluminum matrix is formed that provides acceptable composite bending strength as a result. The presence of chromium and silicon hard inclusions is not a significant obstacle for aluminum plastic flow. Al-Cr and Al-Cr-Si composites produced by hot deformation of the powder mixtures can be used as cathode material for the deposition of wear-resistant nitride coatings on metalworking tools.