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The thermodynamics of five Al3Er compounds were investigated through first-principles density-functional theory (DFT) and experimental analysis. The Al3Er compounds with Al3Ho.hR20 (prototype Al3Ho, Pearson symbol hR20), Cu3Au.cP4, AlNd3.hP8, Ni3Ti.hP16 and Al3Gd.hR12 structures exhibited formation energies of −0.412(−0.417), −0.411(−0.416), −0.400(−0.413), −0.399(−0.345) and −0.342(−0.345) meV/atom when using DFT with “standard” potential (“frozen core” potential) of Er. The results indicated that the Al3Ho.hR20 structure was the thermodynamic stable phase and the other structures were metastable. The formation energy of Cu3Au.cP4 structure was only 1 meV/atom less than that of Al3Ho.hR20. Experimentally, the Al-30 wt.% Er alloys were cooled from 900 °C to 500 °C at the rate of 5 ± 2 °C/h and 60 ± 2 °C/h, respectively. The corresponding XRD analysis showed that the Al3Ho.hR20 was formed at the cooling rate of 5 ± 2 °C/h and the Cu3Au.cP4 was formed at the cooling rate of 60 ± 2 °C/h, which indicated that the Al3Ho.hR20 was in a thermodynamic stable phase and the Cu3Au.cP4 was in a metastable phase with high stability. The structural analysis indicated that the tiny energy difference between Al3Ho.hR20 and Cu3Au.cP4 might be attributed to a similar structure with varied stacking sequences.

The recrystallization behavior of Al-6Mg-0.4Mn-0.15Zr-xSc (x = 0.04, 0.07, 0.10 wt%) alloys was studied using micro-hardness test, optical microscopy and transmission electron microscopy (TEM). The optical micrographs of the alloys with different Sc contents after being annealed at 100–550 °C for 1 h showed that the recrystallized nucleus formed between 275 and 325 °C at the original grain boundaries, and grew quite slowly until 550 °C and above, indicating a 250 °C large span of recrystallization starting and finishing temperatures in the alloys. The TEM observation showed the stripe distributed spherical Al3(Sc,Zr) particles with phase rich region and phase poor region. The recrystallized subgrains with partial HAGBs was found at the phase poor region, but was pinned at the boundary of the phase rich region. The recrystallization driving and pinning pressures of the phase rich regions of the alloys with 0.04 and 0.1Sc wt% were estimated according to Zener drag mode. The results indicated an effective pinning effect of Al3(Sc,Zr) particles on the recrystallized grain at lower than 475 °C. The large span between recrystallization starting and finishing temperatures could be attributed to the stripe distribution of the Al3(Sc,Zr) particles.

Porous SiC composites with lightweight, high strength and low thermal conductivity design can be obtained by constructing porous silicon carbide nanowires (SiCNWs) network and controlling chemical vapor infiltration (CVI) process. The SiCNWs network with an optimized volume fraction (13.6%) and uniform structure is prepared by mixing SiCNWs and polyvinyl alcohol (PVA) firstly. SiCNWs reinforced porous SiC composite (SiCNWs/SiC) with a small uniform pore can be obtained by controlling the chemical deposition kinetics. The morphology of the grown SiC matrix, from the spherical particles to the hexagonal pyramid particles, can be influenced by the deposition parameters like temperature and reactive gas concentration. The strength of the lightweight SiCNWs/SiC composites reach 47.8 MPa with a porosity of 64% and thermal conductivity of 1.2 W/(m∙K), which shows the toughening effect and insulation design with low thermal conductivity.