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This study investigates the mechanical and microstructural properties of aluminum matrix composites (AMCs) reinforced with cobalt-coated carbon nanotubes (CNTs) and Al2024 powder, tailored for aircraft and automotive applications. Using Al7075 alloy as the matrix, composites were fabricated via stir casting, incorporating varying proportions of cobalt-coated CNTs and Al2024 powder. The electroless cobalt coating, applied at thicknesses of 4, 6, 8, and 10 µm, facilitated the uniform distribution and enhanced the compatibility of reinforcements with the Al7075 matrix. Four distinct samples were developed: pure Al7075 alloy, Al7075 with 2 wt.% CNTs, Al7075 with 2 wt.% Al2024 powder, and a hybrid composite combining 2 wt.% of each reinforcement. Microstructural analysis revealed that the 10 µm coating thickness was critical for maintaining reinforcement integrity during the melt phase, preventing crack formation and reinforcement agglomeration. Mechanical testing through vickers hardness and phase analysis using X-ray diffraction analysis, demonstrated that the hybrid composite (A3) exhibited superior hardness and reduced natural aging tendencies compared to its counterparts. Peak aging at 120 °C resulted in the formation of intermetallic compounds like CuAl2 and MgZn2, contributing to improved mechanical properties. These findings highlight the significance of optimizing coating thickness and aging conditions to enhance the performance of AMCs, making them suitable for high-performance applications in the aerospace and automotive industries.

Austempered ductile iron is an innovative material obtained by subjecting it to an austempering heat treatment. The wide application of this material is because its properties are comparable to those of steel, which has a much lower weight. However, the machinability of this material is always a difficult task owing to its high hardness. This problem becomes more complex when a considerable amount of Mn is added. In this study, a novel two-step austempering heat treatment was performed on spheroidal graphite iron containing different amounts of manganese. Although the novel heat treatment method helps to obtain a superior combination of hardness and impact, its effect on machinability must be determined. This study provides the results of machinability tests carried out on austempered ductile iron with various manganese contents produced using the novel method. Scanning electron microscope images of the microstructures revealed a typical ausferrite structure with no segregation of manganese at the grain boundary. This is evident from the good tool life obtained in the machinability tests. Regression equations are fitted to determine the tool life and surface roughness for machining parameters with a range of values considered in this study. The results obtained have shown that till 1 wt% of manganese alloyed austempered ductile iron can be successfully produced using the novel heat treatment method. This helps to obtain the optimum combination of strength and impact properties.

The aim of this work is to investigate the variations in microstructure, hardness, wear and surface roughness between as-cast and heat treated trace elements added A356 alloy. Alloy A was prepared by adding 1 wt.% magnesium to A356 alloy which was used as the base material for the preparation of alloys with zinc (Zn) and copper (Cu) particles as alloying elements. Other set of samples was fabricated where Cu-coated Zn and Cu were added as reinforcements to base matrix A. The microstructural analysis indicated that the addition of Zn to A356 as an alloying element had a limited effect on controlling the grain size during solidification compared to Cu. The addition of Cu as reinforcement resulted in a higher proportion of pro eutectic α-Al phase, leading to finer grain boundaries. Micro-polishing test was conducted on the alloys and composites by determining the surface roughness (Ra) value using profilometer to study the changes in surface roughness under individual load conditions of 20 and 40 N. In the as-cast condition, the addition of Cu increased the hardness by 39% and 58% over the base alloy, respectively. Age-hardening treatment significantly enhanced the wear resistance properties of unreinforced alloys and composites at both aging temperatures, especially at 100 °C. Composite samples exhibited excellent surface finish (lower surface roughness) compared to alloy samples, attributed to the presence of hard reinforcement particles.

Among the various types of recently released composite materials, particle-reinforced metal matrix composites (MMCs), in particular aluminum as the matrix material, have been shown to provide substantial industrial benefits in the automotive and aerospace sectors. The current research focused on the corrosion behavior of an Al7075 hybrid composite in 0.1 M hydrochloric acid (HCl) and 3.5% NaCl media at different temperatures. Electrochemical techniques, such as Tafel polarization (TP) and electrochemical impedance spectroscopy (EIS), were employed to study the corrosion behavior in the respective solutions. The results showed that the corrosion rate of the studied specimen increased from 31.77 to 47.61 mmy−1 in 0.1 M HCl and from 0.26 to 1.28 mmy−1 in 3.5% NaCl with increasing temperature. The corrosion current density of the Al7075 hybrid composite in 0.1 M HCl is on the order of 10−3 Acm2, and that in 3.5% NaCl is on the order of 10−5 Acm2. This confirms the increased rate of composite corrosion in the 0.1 M HCl medium compared to that in the 3.5% NaCl medium. A suitable mechanism was proposed for the corrosion of the Al7075 hybrid composite in both media.

Nowadays, metal matrix composites are being comprehensively used in aero and automotive applications. The usage of composites increased because of their impressive properties viz., improved strength, impact resistance, and tailored features. Compared to uncoated, coated reinforcements in the matrix improves wettability with thinner grain boundary, grain fineness, and the ability for secondary hardening. Improvement in thermal expansion and conductivity makes the composite suitable for moderate temperature shock resistance is the new openings in the field. Conventional liquid stir casting, Rheo-process, and Diffusion roll bonding are some of the methods employed for the processing of composites. Hybridisation of reinforcements with at least one as coated in the matrix improves solid solution strengthening of composites, hence responsible for improved strength and bulk hardness. Generally, a critical literature survey points to copper and nickel coatings. Copper coating rises microhardness, shows poor EMI shielding effectiveness compared to nickel-coated, whereas, nickel-coated reinforcement composites show excellent corrosion resistance compared to that of copper-coated reinforcement. Cobalt-coated nanoparticles reinforced composites upsurges compressive strength and tribological properties compared to nickel-coated ones. However, the extensive review work undertaken collects the possibilities of using different reinforcements in bare state and coated state with or without hybridisation. A comparison of data with property analysis will open the way for further research activities with hybridisation of both or single-coated reinforcements in the matrix and may help to prepare the standard guidelines to advance with a statistical approach. The objective of the present work is to collect the data on the aluminium matrix composites with different reinforcements in coated as well as bare forms and dig on the possibilities for property enhancement.

Austempered ductile iron is an innovative material obtained by subjecting it to an austempering heat treatment. The wide application of this material is because its properties are comparable to those of steel, which has a much lower weight. However, the machinability of this material is always a difficult task owing to its high hardness. This problem becomes more complex when a considerable amount of Mn is added. In this study, a novel two-step austempering heat treatment was performed on spheroidal graphite iron containing different amounts of manganese. Although the novel heat treatment method helps to obtain a superior combination of hardness and impact, its effect on machinability must be determined. This study provides the results of machinability tests carried out on austempered ductile iron with various manganese contents produced using the novel method. Scanning electron microscope images of the microstructures revealed a typical ausferrite structure with no segregation of manganese at the grain boundary. This is evident from the good tool life obtained in the machinability tests. Regression equations are fitted to determine the tool life and surface roughness for machining parameters with a range of values considered in this study. The results obtained have shown that till 1 wt% of manganese alloyed austempered ductile iron can be successfully produced using the novel heat treatment method. This helps to obtain the optimum combination of strength and impact properties. [ABSTRACT FROM AUTHOR]

This technical paper demonstrates the possibilities of nickel (Ni) coated Al2024 powder reinforcement in an Al7075 matrix using the liquid stir casting technique. Additionally, the paper focuses on achieving stable properties by implementing artificial aging heat treatment. To apply the Ni coating, the electroless nickel plating technique was utilized, and a minimum coating thickness of 8 μ m was determined to effectively prevent the dissolution of Al2024 powder reinforcements within the Al7075 matrix. Stir casting facilitated the uniform dispersion of the coated Al2024 powder up to a weight percentage of 7%. Subsequently, the Al7075 alloy and composites underwent artificial aging through solution heat treatment (SHT) at 450 °C for 4 h, followed by water quenching and aging at temperatures of 120, 150, and 180 °C. Aging at 120 °C was found to yield superior results compared to aging at 150 and 180 °C, thus identified as the optimum aging temperature. When the Ni coating thickness was increased beyond the optimal 8 μ m, the resulting enhancements in hardness for both as-cast and peak-aged specimens, as well as the tensile strength, were not significant. The improvements observed were only marginal, ranging between 2 to 3%. Fracture surface analysis revealed that the predominant fracture mode in the Al7075 alloy was ductile, characterized by dimple rupture. In the as-cast Al7075-(7%, 8 μ m) Al2024 composite, a mixed fracture mode comprising both brittle and ductile characteristics was observed. In the peak-aged (120 °C) Al7075-(7%, 8 μ m)Al2024 composite, the overall fracture mode exhibited a dominant brittle nature. Analytical techniques including XRD, TEM, and EDS confirmed the presence of Mg _2 Si, MgZn _2 , CuAl _2 , and CuAl _2 Mg phases in the peak-aged (120 °C) Al7075-(7%, 8 μ m) Al2024 composite. These phases contributed to the enhancement of the properties of both the Al7075 alloy and its composites. The developed composites can be used in automobile parts and aerospace applications.