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The influence of partial substitution of Hf for Zr on the microstructure and thermal stability of near‐α high‐temperature titanium alloys is systematically investigated. The results show that the addition of Hf promotes the refinement of precipitated phases of the silicides and α2 phase and the (Ti,Zr,Hf)6(Si,Sn)3 S2‐type silicides were formed in alloys after aging treatment. During thermal exposure, both silicides and α2 phase in alloy with 2.5 wt% Hf exhibited excellent anti‐coarsening ability, which may be attributed to the slow diffusion of Hf in Ti that significantly inhibited the growth rate of the precipitated phase. The loss of plasticity of near‐α titanium alloys after thermal exposure is mainly due to the precipitation and coarsening of silicides and α2 phase, therefore, the Hf‐containing titanium alloy has more excellent thermal stability, i.e., the plasticity loss rate is decreased from 34.8% (the alloy without Hf) to 7.4% (the alloy with 2.5 wt% Hf). [ABSTRACT FROM AUTHOR]

• Phase size is different in as-SLMed Ti-6Zr-5Fe alloy, especially α phase size. • Phase composition and size are different in as-solutionized Ti-6Zr-5Fe alloy. • Gap of microhardness between top and bottom decreases after solution treatment. • Gradient microstructure or property in near-β Ti alloy can be obtained. The homogeneity of microstructure and microhardness in different parts of as-fabricated selective laser melting (SLM) and as-solutionized Ti-6Zr-5Fe alloy is presented in this paper. The results show that the as-fabricated SLM alloy has a bigger β phase and finer α phase size in the top part than that in the bottom part due to the reheating treatment during SLM process. However, as-solutionized Ti-6Zr-5Fe alloy mainly consists of β phase in the top part, and the bottom part is mainly comprised of β and α phase in the grain boundary. Apart from the change of phase composition, the β phase size in bottom part is smaller than that in the top part, due to the precipitation of α phase at the grain boundary in the bottom part. The fine α phase in the top part of as-fabricated SLM Ti-6Zr-5Fe alloy results in that the top part has a higher microhardness (518 HV) than the bottom part (394 HV). While, the microhardness becomes almost the same in the top part (482 HV) and bottom part (475 HV) after solid solution treatment. The dissolution of fine α phase in the top part and solution strengthening of Fe and Zr element in the bottom part after solution treatment improve the uniformity of microhardness. This research provides an approach for obtaining the gradient microstructure or gradient property for near-β Ti alloy samples by governing the parameters of SLM technology and solution treatment. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) process belongs to a layer-by-layer additive manufacturing technology, which has different temperature gradients, cooling rates, and reheating treatment in different regions due to the variation of the thermal histories for different layers during SLM process. This work aims to study the microstructural homogeneity evolution of β phases, such as size, morphology, distribution, crystallographic orientation, and phase composition in different regions of the SLM Ti-6Zr-5Fe near β titanium alloy. The results indicate that the microstructure in different regions of SLM Ti-6Zr-5Fe alloy sample is quite different. The β phase in the bottom area had the smallest size about 7.25 μm, the β phase in the side-top area had the largest size about 20.56 μm. The β phase in the side-middle and middle part had a lower aspect ratio of 1.52 and 1.59, the β phase in the side-bottom and top part had a larger aspect ratio of 1.93 and 1.92. Most of the β phase in the side-bottom and top part had the 〈001〉 crystal orientation towards build direction and laser moving direction, the texture type in other regions was random. The α phase in the top of the SLM Ti-6Zr-5Fe sample had a smaller size than that in the middle and bottom of the sample. Meanwhile, the microhardness in the top of SLM Ti-6Zr-5Fe sample was higher than that in the middle and bottom of the sample. The temperature gradients, cooling rates, and reheating treatment play different leading roles in different regions of the SLM Ti-6Zr-5Fe alloy sample. • β phase size, morphology, crystallographic orientation are not entirely the same. • α phase size in middle and bottom is larger than that in the top. • Microhardness in the top is higher than that in the middle and bottom. • Temperature gradients, cooling rates, reheating treatment play different roles. [ABSTRACT FROM AUTHOR]

In this paper, semi‐solid Al–7Si–0.4Mg–x erbium(Er) (x = 0, 0.1, 0.3, 0.5, 0.8 wt%) alloys are fabricated via electromagnetic stirring method. The effects of Er on the microstructures and mechanical properties of semi‐solid Al–7Si–0.4Mg alloys are investigated. Results show that the eutectic π‐phase is modified to fine sized Er‐poor π‐phase and primary α‐Al is refined in semi‐solid Al–7Si–0.4Mg alloys with the addition of Er. Meanwhile, the plate‐like shape eutectic Si is transformed into fibrous eutectic Si with addition of Er, which has an excellent modification effect on the eutectic Si. Nucleation rate of the Er‐poor π‐phase is increased with a higher super cooling rate, which causes the refinement of primary α‐Al and the modification of eutectic Si phase. With the addition of 0.3 wt% Er, semi‐solid Al–7Si–0.4Mg alloys obtain the best tensile properties. The ultimate tensile strength and elongation values are 228 MPa and 10.4%, which is increased by 7% and 50% than Er‐free alloy, respectively. With the addition of Er into semi‐solid Al–7Si–0.4Mg alloys, the Chinese script π‐Fe phase is modified to fine size and globule Er‐poor π‐phase. The addition of 0.3% Er to semi‐solid Al–7Si–0.4Mg alloy improves the tensile strength about 7%, especially elongation (50%), which is attributed to the combined action of eutectic Si modification, primary α‐Al grain refinement, and π‐phase modification. [ABSTRACT FROM AUTHOR]

Abstract: The annealing behavior of a modified 5083 aluminum alloy was studied in the temperature range of 125–375°C with different holding times. The results shown that the annealing temperature was more sensitive to the mechanical and corrosion resistance properties compared with the annealing holding time. The mechanical and corrosion resistance properties depend on annealing treatment due to different dislocation configuration in the matrix and the second phase interface, annealing temperature and time have been optimized for both of those properties improvement. [Copyright &y& Elsevier]