Microstructure and Lattice Parameters of AlN Particle-Reinforced Magnesium Matrix Composites Fabricated by Powder Metallurgy

doi:10.1007/s40195-015-0333-6

Abstract

Abstract:

Magnesium matrix composites reinforced with AlN particles were fabricated by the powder metallurgy technique. The evolution of lattice constants and solid solubility levels of Al in α-Mg and the microstructure of Mg-Al/AlN composites were investigated in the present study. The results showed that the solid solubility of Al in α-Mg reached a relatively high level by the P/M process with a long time of milling. X-ray diffraction showed that the peaks of Mg phase clearly shifted to higher angles. The lattice constants and cell volume decreased significantly compared with those of standard Mg due to a significant amount of Al incorporated into α-Mg in the form of substitutional solid solution. The degree of lattice deformation decreased at a low sintering temperature and increased at higher sintering temperatures due to the presence of AlN. Microstructural characterization of the composites revealed a necklace distribution of AlN particles in the Mg matrix. Heat treatment led to precipitation of Mg₁₇Al₁₂ from the supersaturated α-Mg solid solution. The precipitate exhibited granular and lath-shaped morphologies in Mg matrix and flocculent precipitation around AlN particles.

Key words: Metal matrix composite, AlN particle, Microstructure, Lattice parameter, Powder metallurgy, Solid solubility

Jie Chen, Chong-Gao Bao, Yong Wang, Jin-Ling Liu, Challapalli Suryanarayana. Microstructure and Lattice Parameters of AlN Particle-Reinforced Magnesium Matrix Composites Fabricated by Powder Metallurgy[J]. Acta Metallurgica Sinica (English Letters), 2015, 28(11): 1354-1363.

Figures/Tables 12

Fig. 1 XRD patterns of Mg-Al powder mixture a and Mg-Al/AlN powder mixture after milling b

Fig. 2 XRD patterns of Mg-Al alloys and Mg-Al/AlN composites sintered at different temperatures

Fig. 3 Shifting of Mg peaks in Mg-Al alloys and Mg-Al/AlN composites at different sintering temperatures

Table 1 Lattice parameters of Mg in the Mg-Al alloys and the Mg-Al/AlN composites sintered at different temperatures, where A and C represent Mg-Al alloy and Mg-Al/AlN composite, respectively

Lattice parameter	Standard Mg	A-550 °C	A-585 °C	A-620 °C	C-550 °C	C-585 °C	C-620 °C
a (nm)	0.32088	0.31836	0.31881	0.31894	0.31873	0.31907	0.31889
c (nm)	0.52099	0.51750	0.51815	0.51831	0.51812	0.51810	0.51806
Cell volume (nm³)	0.04646	0.04542	0.04561	0.04566	0.04558	0.04568	0.04562
c/a	1.6236	1.6255	1.6253	1.6251	1.6256	1.6238	1.6246

Fig. 4 Shrinkage levels of Mg cell for both the Mg-Al alloys and Mg-Al/AlN composites at different sintering temperatures

Fig. 5 SEM micrographs of initial starting powders (Mg, Al and AlN) before milling and the powder mixtures of Mg-Al/AlN after milling (powder mixture and surface of magnesium)

Fig. 6 Microstructure and EDS analysis of Mg-Al/AlN composites fabricated by P/M process

Fig. 7 Optical micrographs of Mg-Al/AlN composites with different magnifications: a overall microstructure; b distribution of AlN

Fig. 8 Concentration variation of Mg and Al elements across this region in the Mg-Al/AlN composites (numbers 1 and 2 represent the center of the grain boundary and AlN, respectively)

Fig. 9 Micrographs of β-Mg17Al12 phase in Mg-Al alloys a and Mg-Al/AlN composites b

Fig. 10 Morphologies of Mg17Al12 precipitation after annealing at 200 °C for 10 h of Mg-Al alloys a, matrix of Mg-Al/AlN composites b and around AlN particles c, and EDS results of the marked areas (the samples were gold-sputtered before observation)

Table 2 Calculated solubility limit of Al in Mg for Mg-Al alloys and Mg-Al/AlN composites sintered at different temperatures, where A and C represent Mg-Al alloy and Mg-Al/AlN composite, respectively (in at.%)

A-550 °C	A-585 °C	A-620 °C	C-550 °C	C-585 °C	C-620 °C
6.5099	5.3473	5.0351	5.4764	5.0675	5.3274

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