Dynamic recrystallization behavior and mechanical properties of bimodal scale Al2O3 reinforced AZ31 composites by soild state synthesis

In this paper,(500 nm 1%+5μm 3%)bimodal scale Al2O3p/AZ31 composites was fabricated by solid state synthesis and the effect of bimodal scale Al2O3 particulates on its dynamic recrystallization behavior and mechanical properties was investigated.The optical microscopy,scanning electron microscopy,transmission electron microscopy and electron universal strength tester composites were used to characterize the composites.The results indicate that the grains size of the composites are significantly refined and the mechanical properties are obviously improved.Due to the presence of the bimodal scale Al2o3 particulates,the high-density dislocation zone is formed around nano-Al2o3p and the particle deformation zone is formed near micron-ABOap.These zones are ideal sites for the formation of recrystallization nucleus.Meanwhile,the addition of the bimodal scale Al2o3 particulates may delay or hinder the growth of matrix grain through the pining effect on the grain boundaries,resulting in significantly improving the yield strength and tensile strength of Al2O3p/AZ31 composites.

Influence of particulate morphology on microstructure and tribological properties of cold sprayed A380/Al2O3 composite coatings

In this study,three kinds of A380/Al2O3 composite coatings were prepared by cold spray(CS)using spherical,irregular and spherical+irregular shaped Al2O3 particulates separately mixed in the original A380 alloy powders.The influence of Al2O3 particulates’morphology on the microstructural characteristics(i.e.retention of Al2O3 content in coatings,coating/matrix interfacial bonding,pore size distribution and morphology etc.)and wear performance of the coatings was investigated by scanning electron microscopy(SEM),X-ray computed tomography(XCT)and 3-D optical profilometry.Results indicated that the spherical Al2O3 showsobvious tamping effect during deposition process.As a result,the interfaceshowedawavy shape while the matrix and particulates were mechanical interlocked with much improved adhesion.In addition,the porosity of the coating was minimized and the pores exhibited curved spherical structure with reduced dimensions.The irregular Al2O3 particles predominantly displayed the embedding effect together with fragmentation of Al2O3 particulates.Consequently,poor coating/matrix interfacial bonding,high porosity and the formation of angular-shaped pores were resulted in the coating.Dry sliding wear tests results revealed that the wear resistance of the coating is directly related with the retained content of Al2O3 in the coating.The coating containing irregular Al2O3 particulates displayed superior wear performance with its wear rate one seventh of that of the pure A380 alloy coating.The coating containing both kinds of Al2O3 particulates showed mixed characteristics of above two kinds of Al2O3 composite coatings.

Effect of Si content on impact-abrasive wear resistance of Al2O3p/steel composites prepared by squeeze casting

The 40Cr steel matrix composites were reinforced with Al203 particulates （Al2O3p） through Si adding to improve the impact-abrasive wear resistance, in which Si powder ranging up to 25% of the AlzO3p weight was added into the Al2O3p preforms; then, the composites were fabricated by squeeze casting. For all composites, alumina particles are evenly distributed, and Si powder is dissolved in the matrix. Without Si powder addition, the 40Cr steel matrix contains only pearlite; however, ferrite appears and increases with Si powder addition. In the impact-abrasive wear tests, the impact frequency is 80 min^-1 and the impacting energy is 2 J. With increasing Si powder, the wear of the composites first decreases obviously, reaches the minimum at 10% and then increases. The effect of Si addition on the wear resistance can be attributed to two reasons： one is increasing the hardness of the matrix, and the other is improving the interfacial bonding between Al2O3p and steel. The wear mechanism of the composites is abrasive wear when the Si powder is 〈 10 wt%. Otherwise, it is a mixed mode of abrasive and delamination wear.