Effect of Sintering Temperature on Microstructure and Mechanical Properties of AZ91 Magnesium Alloy via Spark Plasma Sintering

Abstract

AZ91 alloy is the commonly used magnesium alloy due to its castability and high specific strength. [1,2] However, the cast AZ91 alloy shows low absolute strength and poor ductility due to large grain size, coarse precipitates, and close-packed hexagonal (HCP) structure, which greatly hinder its application. [2][3][4] Grain refinement is one effective way to improve the mechanical properties of Mg alloys. Plastic deformation technology is an important approach for grain refinement of magnesium alloys. It is well accepted that the strong basal texture forms in plastic deformation processing. However, when compressed along the rolling direction or extrusion direction, the {1012} tension twinning is activated, resulting in a relatively low compressive yield strength (CYS). [5] Thus, tension twin suppression is an important issue for improving compressive properties of Mg alloys. Grain refinement and texture weakening are two effective strategies for tension twin suppression. As an innovative processing technology, spark plasma sintering (SPS) combines high uniaxial pressure with pulsing direct electric current to heat the powder, which achieves the densification of sintered samples in a short time and forms a finer microstructure without texture. [6][7][8] Furthermore, SPS technology has been used to fabricate fine-grain Mg alloys with high compressive strength compared with the cast Mg alloys. [9][10][11] Recent researches showed that the mechanical properties of magnesium alloy are determined by the grain size, amount of precipitates, and solute content, which are greatly related to the sintering temperature. [10][11][12] The grain refinement, precipitation, and solid solution strengthening mechanisms have been developed to explain the impact of microstructure on the mechanical properties of the SPS-sintered magnesium alloys. [10] In addition, the dislocation strengthening mechanism plays an important role in metals with high density of dislocations. [13][14][15] It should be noticed that the gas-atomized powder contains a high degree of dislocations. [16] However, there is little report on the evolution of dislocations density at different sintering temperatures for SPS Mg alloys. Consequently, the effect of dislocation strengthening on the mechanical properties of the SPS-sintered magnesium alloys is yet not clear.In this work, gas-atomized powder was used to prepare AZ91 alloys by SPS. This study aims to quantitatively investigate the effect of the SPS sintering temperature on the microstructure (the amount and distribution of precipitates, the dislocation density, and the grain size) and the mechanical properties of the

Empirical Prediction of Optimum Process Conditions of Spark Plasma-Sintered Magnesium Composite (AZ91D-Ni-GNPs) Using Response Surface Methodology (RSM) Approach

“…Also, the interaction of the surface of the sample with the environment during metallography results in the formation of oxides observed in Figure 13 ac. By comparing the sintered relative density and theoretical density, the relative densities obtained were greater than 97% density for samples A, B, and C, which implies that the sintering parameters used are appropriate in this study [43]. As reported by Zhu G. et al [35], the combination of high sintering temperature and pressure is responsible for the high densification.…”

“…The process parameters were set according to the Design of Experiment (DoE)-RSM developed. The selection of the process parameters utilized in the DoE-RSM is based on a similar study in the literature on the manufacturing of AZ91D Mg powder (matrix) [42,43].…”

“…Although, there is a marginal difference between the average value of the grain size for the three samples with nearly the same relative density, the increasing average grain size with increasing sintering temperature influence the hardness property of the composites. In the studies of Zhu Y. et al [43], sintering temperature between 350 and 450 ℃ was used in the SPS of AZ91 magnesium alloy, and Minarik P et al [52] used sintering temperature between 450 and 550 ℃ to develop AE42 magnesium alloy using SPS. They both reported that an increase in sintering temperature increases the average grain size in the sintered components, even with sintered materials having nearly the same relative density.…”

“…The changes indicate that sintering occurred through recrystallization, neck formation, and grain growth, which consequently lead to high densification. The large micropores formed at the contact points between two or more spherical particles disappeared during sintering [53], suggesting that the parameters used are appropriate for developing dense AZ91D-Ni-GNPs magnesium-based composites.…”

Simultaneous Improvement of the Strength and Plasticity for Ti‐Reinforced Fine‐Grained Magnesium Matrix Composites Prepared by Powder Metallurgy

“…[20] This method enables the fabrication of fully dense components with a finer microstructure, requiring lower sintering temperatures and shorter sintering times compared to other PM methods. [21,22] Therefore, it is expected to become an effective approach to develop high-performance magnesium alloys by combining the designability characteristic of the MMCs and the unique advantages of the SPS technique. Wu and co-workers [23] prepared Ti particle-reinforced AZ91 composites by the SPS.…”