The effect of Sc-microalloying and Y₂O₃ nano-particles on the microstructure and mechanical properties of as-cast Al-5.5Si alloy is studied by means of optical microscopy, transmission electron microscopy, hardness test and tensile test. The influence of annealing treatment on the microstructure and properties of the Al-Si alloys is also investigated as well. The results show that the addition of Sc and Y₂O₃ nano-particles could significantly improve the mechanical property of the Al-Si alloy. The ultimate tensile strength and yield strength of Al-Si-Sc/Y₂O₃ alloy are improved by around 45 and 71%, respectively, when compared to that of the Al-Si alloy. The effect of the nanosized particles (precipitated and added) on strengthening and deformation of Al-Si alloy is analyzed and discussed in detail. The results of annealing treatment indicate that the change in mechanical property of the Al-Si-Sc alloy during annealing treatment is mainly associated with the precipitation of the secondary Si phase. Graphical Abstract

High-purity magnesium (Mg) is a promising biodegradable metal for oral and maxillofacial implants. Appropriate surface roughness plays a critical role in the degradation behavior and the related cellular processes of biodegradable Mg-based metals. Nevertheless, the most optimized surface roughness has been questionable, especially for Mg-based oral and maxillofacial implants. Three representative scales of surface roughness were investigated in this study, including smooth (Sa < 0.5 µm), moderately rough (Sa between 1.0–2.0 µm), and rough (Sa > 2.0 µm). The results indicated that the degradation rate of the Mg specimen in the cell culture medium was significantly accelerated with increased surface roughness. Furthermore, an extract test revealed that Mg with different roughness did not induce an evident cytotoxic effect. Nonetheless, the smooth Mg surface had an adversely affected cell attachment. Therefore, the high-purity Mg with a moderately rough surface exhibited the most optimized balance between biodegradability and overall cytocompatibility.

In order to investigate the effect of Mg₂Si formation on the microstructure and properties of an Al−Si alloy, the critical point of a hypereutectic Al−17Si−4Cu−Mg alloy was calculated by Pandat software. The calculation results of the equilibrium phase diagram show that the critical point for Mg₂Si phase formation for the alloy was obtained when the Mg content was 2.2%. The contents of 0.5 wt.% Mg and 2.5 wt.% Mg were selected as the research object. The content of Mg increased from 0.5 wt.% to 2.5 wt.%, the eutectic Si in the matrix was reduced, and the Chinese character-like Mg₂Si phase appeared in the microstructure. In the peak ageing state, in addition to θ″ and Q′ phases that were mainly precipitated, there was also needle-like β″ precipitation in the 2.5 wt.% Mg content alloy. Larger precipitates were found in 2.5 wt.% content alloys, mainly due to the promotion of the solid solution having the aggregation and segregation of more solute elements in the matrix. The tensile strength, elongation, and hardness of hypereutectic Al−17Si−4Cu−0.5Mg alloy under peak ageing were 331 MPa, 3.11%, and 152.1 HB, respectively. The tensile strength and the elongation decreased while the hardness increased with the 2.5 wt.% Mg content, which is due to the formation of hard and brittle Mg₂Si and Al₈FeMg₃Si, which has a splitting effect on the matrix.

Hierarchically porous hydroxyapatite (HHA) scaffolds were synthesized by template-assisted sol-gel chemistry. Polyurethane foam and a block copolymer were used as templates for inducing hierarchically porous structures. The HHA scaffolds exhibited open porous structures with large pores of 400–600 µm and nanoscale pores of ~75 nm. In comparison with conventional hydroxyapatite (CHA), HHA scaffolds exhibited significantly higher surface areas and increased protein adsorption for bovine serum albumin and vitronectin. Both the HHA and CHA scaffolds exhibited well in vitro biocompatibility. After 1 day, Saos-2 osteoblast-like cells bound equally well to both HHA and CHA scaffolds, but after 7 days in culture, cell proliferation was significantly greater on the HHA scaffolds (p < 0.01). High surface area and hierarchical porous structure contributed to the selective enhancement of osteoblast proliferation on the HHA scaffolds.

In this work, based on the A356 alloy, a novel Al–Si–Mg–Cu–Fe–Sr alloy with good mechanical property and high thermal conductivity was developed. The semi-solid slurry of the alloy was prepared via the vibrating contraction inclined plate. The microstructure evolution and solidification behavior of the alloy were investigated. The results demonstrated that, compared with the A356 alloy, the enhanced property of the Al–Si–Mg–Cu–Fe–Sr alloy was associated with the size of primary α-Al grains and morphology of eutectic Si phases. In addition, the preparation process parameters of semi-solid slurries, including the pouring temperature, inclination angle, and vibration frequency, had a crucial effect on the size and morphology of primary α-Al grains. The optimized pouring temperature, inclination angle, and vibration frequency were 670 °C, 45°, and 60 Hz, respectively. In this condition, for the primary α-Al grains, a minimum grain diameter of 64.31 µm and a maximum shape factor of 0.80 were obtained. This work provides a reference for the application of the alloy with high performance in the field of automobile and communication.

To reveal the formation and wear mechanisms of rheo-formed aluminum alloy - B₄C composites, A356 alloy − 10 mass% B₄C composite material was fabricated by semi-solid stirring rheo-casting and rolling process. The presence of Al₃BC was confirmed by XRD analysis and hinted that chemical bonding formed at interfaces between aluminum matrix and B₄C particles. Tensile test results demonstrated that addition of B₄C facilitated improving the tensile strength by refining matrix and providing particle strengthening. Failure tests revealed that the failure type of the composite transferred from interfacial debonding to particle cracking with increasing wear load. The wear rate of the composite was approximately 48% lower than that of aluminum alloy under 60 N load. The friction coefficient of the composite under 60 N load also significantly decreased due to formation of B₂O₃and H₃BO₃as solid lubricants.