Microstructural characterization and mechanical properties of friction surfaced AA2024-Ag composites

The effects of Ag on the microstructure, mechanical properties, and electrical conductivity of AA2024 aluminum alloy coating were investigated. It was fabricated by friction surfacing as an additive manufacturing process. To carry out this investigation, Ag was added by 5.3, 10.6, and 16.0 wt.% to an AA2024 consumable rod by inserting holes in it. It was found that due to the strengthening by solid solution and the formation of precipitates and intermetallic containing Ag, the driving force for grain growth is reduced and consequently the grain size of the coating is decreased. After artificial aging heat treatment, the electrical conductivities of the coatings containing 0 and 16.0 wt.% Ag are increased by 4.15%(IACS) and decreased by 2.15%(IACS), respectively. While considering a linear relationship, it can be proposed that for a 1 wt.% Ag increase, the strength and hardness of the coating will be increased by 1.8% and 1.0%, respectively. It was established that the effect of Al6(Cu,Ag)Mg4 precipitate formation on strengthening is greater than that of Ag-rich intermetallic.

Aging Behavior of Nano-SiC/2014Al Composite Fabricated by Powder Metallurgy and Hot Extrusion Techniques

The aging-hardening kinetics of powder metallurgy processed 2014Al alloy and its composite have been studied. The existence of n-SiC particulates leads to the increase of peak hardness. Interestingly, the aginghardening peak of the composite takes place at earlier time than that of the unreinforced alloy. Transmission electron microscopy（TEM） studies indicated that the major precipitation phases are Al_5Cu_2Mn_3 and θ′（Al_2Cu）. Besides, Ω phase appeared in both specimens at peak hardening condition, which has been rarely observed previously in aluminum metal matrix composites without Ag. Accelerated aging kinetics and increased peak hardness may be attributed to the higher dislocation density resulted from the mismatch of coefficients of thermal expansion between n-SiC and 2014Al matrix. The results are beneficial to fabricating high performance composites for the application in automobile field such as pistons, driveshaft tubes, brake rotors, bicycle frames, railroad brakes.

Improvement of mechanical properties, microscopic structures, and antibacterial activity by Ag/ZnO nanocomposite powder for glaze-decorated ceramic

With the increase in the international trade of ceramics, improvement in the physical and chemical properties of ceramics has become a market demand in recent years. The addition of nanomaterials in glaze can simultaneously improve the mechanical and corrosion resistance properties of ceramics. In this study, the effect of nano-sized Ag/ZnO in glazed ceramic was investigated considering the hardness, whiteness, and microscopic structures of the products. Results showed that the Ag/ZnO nanocomposite powder significantly affects the performance of glaze. Glaze hardness reached the highest value (96.6 HV) at the low sintering temperature of 1130 ℃ with the addition of 10% Ag/ZnO nanocomposite powder. Furthermore, the Ag/ZnO nanocomposite powder improved crack resistance and whiteness. Ag as AgO and Ag2O in the glaze was effective for antibacterial activity of ceramic. In addition, the Ag/ZnO nanocomposite powder could also promote the shrinkage of bubbles in the glaze layer and smooth the glaze. These results indicated that the nanoparticles could act as an active center for melting raw materials, which is crucial for ceramic properties.