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5xxx series aluminum alloys have been widely used in automobiles, ships, aerospace and other fields for their low density, good corrosion resistance and weldability. The present study designs a new Al-10.0Mg-1.0Zn-0.15Cu (wt%) alloy with different composition from the traditional 5xxx series and 7xxx series aluminum alloys; the Zn/Mg ratio is below 1.0. Detailed characterization by scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM) has been carried out to reveal the microstructural evolution. The results show that the addition of Zn and Cu inhibits the precipitation of the Al3Mg2 phase in the traditional Al-Mg binary alloy during annealing and promotes the precipitation of T-Mg32(Al,Zn)49 phase, which contributes to precipitation strengthening. After 75% rolling and 150 °C annealing, the T-Mg32(Al,Zn)49 phase precipitates and the alloy obtains good strength and plasticity coordination with 0.2% offset yield strength of 519 MPa and ultimate tensile strength of 653 MPa, accompanied by uniform elongation of 8.1%. The mechanisms underlying the improved strength and plasticity in the Al-10.0Mg-1.0Zn-0.15Cu (wt%) alloy are discussed. [ABSTRACT FROM AUTHOR]

We report a systematic study on the influence of Cr removal on the microstructure and mechanical behaviour of an ultra-fine grained (UFG) high-entropy alloy (HEA), Al0.8Ti0.2CoNiFeCr, fabricated via spark plasma sintering (SPS) of mechanically alloyed (MA’ed) powders from constituent elemental powders. The MA’ed Al0.8Ti0.2CoNiFeCr powders consist principally of a BCC phase (∼85 vol.-%) with a small amount of FCC phase (∼15 vol.-%), whereas the MA’ed Al0.8Ti0.2CoNiFe powders present similar phases to those in the MA’ed Al0.8Ti0.2CoNiFeCr powders. Interestingly, the SPS processed UFG Al0.8Ti0.2CoNiFeCr alloy contains mostly an FCC phase (∼78 vol.-%) and some BCC phase (∼22 vol.-%); in contrast, the SPS processed UFG Al0.8Ti0.2CoNiFe alloy consists of a slightly enriched BCC phase (∼53 vol.-%) and an FCC phase (∼47 vol.-%). In addition, the SPS processed Al0.8Ti0.2CoNiFe alloy exhibits slightly higher yield strength, compressive strength and hardness but lower plasticity than those of the SPS processed Al0.8Ti0.2CoNiFeCr alloy. Special theme block on high entropy alloys, guest edited by Paula Alvaredo Olmos, Universidad Carlos III de Madrid, Spain, and Sheng Guo, Chalmers University, Gothenburg, Sweden. [ABSTRACT FROM AUTHOR]

The objective of the present study is to explore the feasibility of producing 7075 Al alloy ribbons with the increased microhardness via rapid solidification processing, namely melt spinning. Our results show that the melt spun+aged 7075 Al alloy ribbons exhibit approximately 17% (307 MPa) higher microhardness than that of the coarse-grained (CG) counterpart solid-solution treated+aged under the same conditions. The higher microhardness of the melt spun+aged 7075 Al alloy stems from its microstructural features, including (i) sub-micrometric/micrometric sized grains, (ii) intragranular subgrains, and (iii) nanoscale precipitates with inter-precipitate distance slightly smaller than that in the CG counterpart. In an effort to understand the microstructure in melt spun+aged 7075 Al alloy, the microstructural evolution during aging of the as-melt spun 7075 Al alloy was analyzed and discussed. By quantifying the contributions of precipitation, grain boundary, dislocation, solid solution and subgrain boundary strengthening to the yield strength based on the microstructural analysis, the higher microhardness of the melt spun+aged 7075 Al alloy ribbons was rationalized. [ABSTRACT FROM AUTHOR]

In an effort to further improve the strength of 7000 series commercial Al alloys relative to that of the solid-solution treated plus aged ones, the microstructure and microhardness of an as-melt spun 7075 Al alloy were studied. Our results indicate that the as-melt spun 7075 Al alloy is characterized by sub-micrometric/micrometric sized grains that contain a density of dislocations 5.7 × 10 13 m −2 , and it exhibits much higher microhardness than that of the solid-solution treated coarse-grained counterpart. The factors that affect grain size and dislocation density were analyzed and discussed. Based on the calculations of the contributions of grain boundary and dislocation strengthening to the overall strength, higher microhardness of as-melt spun 7075 Al was rationalized. [ABSTRACT FROM AUTHOR]

This paper reports a study on the microstructure and hardness of an as-melt spun Al–Mg alloy as a potential material used for micro-manufacturing. Our results show that the microstructure is characterized by a nearly single-phase fine-grained Al-based supersaturated solid solution containing a relatively high density of dislocations and the as-melt spun Al–Mg alloy exhibits a much higher microhardness relative to that of the coarse-grained counterpart. The quantitative relationship between microhardness and microstructure was established by quantifying the contributions of various strengthening mechanisms. [ABSTRACT FROM AUTHOR]

To attain an unusual combination of low density and high specific strength in lightweight materials, Ti–Mg heterostructured (HS) materials comprising soft Mg domains embedded in hard Ti domain matrix were developed. Unlike hitherto reported HS materials, Ti–Mg HS materials are characterized by: (i) significant difference in coefficient of thermal expansion (CET) between soft Mg and hard Ti domains, and (ii) soft Mg domains having lower ductility. The influences of the two features on strength and ductility of HS materials remain poorly understood. To address these questions, this paper reports studies on microstructure and mechanical properties of the Ti–Mg HS materials. The Ti–Mg HS materials were prepared by spark plasma sintering of the mixture of Ti and Mg elemental powders. Ti–12Mg achieves tensile yield strength higher than that calculated using the rule-of-mixture and uniform elongation higher than that of cast Mg. Ti–15Mg obtains tensile yield strength higher than that calculated using the rule-of-mixture but uniform elongation lower than that of cast Mg. Each of Ti–20Mg and Ti–29Mg exhibits tensile yield strength lower than that calculated using the rule-of-mixture and uniform elongation lower than that of cast Mg. The mechanisms underlying strength and ductility of these Ti–Mg HS materials were revealed by analyzing the combined effects of heterogeneous deformation induced strengthening and work-hardening with stress concentration originating from the presence of cracks at Ti/Mg domain boundaries as a result of notable difference in CET between Ti and Mg. [ABSTRACT FROM AUTHOR]

In this study, we report on the influence of high pressure on the microstructure evolution of cryomilled nanostructured Al alloy powders during spark plasma sintering (SPS). Our experimental results suggest that the particular mechanism that governs grain growth during SPS depends on the magnitude of the applied pressure. In the case of material consolidated at a high pressure (e.g. 500 MPa), grain coarsening occurs via a combination of thermally activated grain boundary (GB) migration, stress-coupled GB migration and grain rotation-induced grain coalescence. In contrast, in the case of the material consolidated at a low pressure (50 MPa), grain growth occurs primarily via thermally activated GB migration. [ABSTRACT FROM AUTHOR]

We describe an investigation on spark plasma sintering (SPS) of micrometric-sized (1–10 μm) Al powders and the associated microstructures and tensile properties of the consolidated Al. Our results show the presence of disrupted nanoscale oxide particles at grain boundaries (GBs) and micrometric-sized grains and a combination of high strength and acceptable ductility in the Al SPS-ed above 580 °C. Our research was motivated by the fact that the mechanisms underlying the disruption of oxide films and the formation of a metallurgical bond between Al powders during SPS, and the effects of the disrupted nanoscale oxide particles on grain size and mechanical properties in the consolidated Al, hitherto remain poorly understood. By investigating the densification mechanisms underlying SPS of Al powders and microstructure of the consolidated Al, we suggest that the disruption of oxide films can be primarily attributed to the action of a spark discharge; correspondingly, the metallurgical bond between Al powders results from the fusion of molten Al in the vicinity of neighboring Al powder surfaces. Based on calculations using a previously developed model, grain growth was impeded as a result of negative net driving forces for GB migration and grain rotation due to the presence of the nanoscale oxide particles at GBs. On the basis of a Hall-Petch mechanism, the high strength was rationalized by the micrometric-sized grains and the enhanced Hall-Petch slope. Based on microstructure of the consolidated Al, the acceptable ductility was attributed to a minimization in stress concentration due to the nanometric sizes of the oxide particles and the presence of ductile grain interiors. [ABSTRACT FROM AUTHOR]

We report on a study of the microstructure and mechanical behavior of a bulk nanostructured (NS)/ultra-fine grained (UFG) aluminum fabricated by cryomilling and high-pressure spark plasma sintering (SPS). The compressive yield stress of the consolidated material is determined to be 380 MPa, which is significantly higher than that of commercial strain hardened aluminum (124 MPa). Microstructural studies reveal that the nanometric grains are embedded inside a matrix of ultra-fine grains in the bulk material. The corresponding average grain size is approximately 125 nm and with a distribution of grains that are smaller than 500 nm. Moreover, chemical analysis of the powder particles and the consolidated samples indicates that carbon and oxygen levels remain unchanged, and that there is a slight decrease in the nitrogen level and a significant reduction in the hydrogen level after spark plasma sintering. Semi-quantitative analysis suggests that the mechanisms that contribute to the strength of the consolidated material include: grain boundary strengthening, second phase strengthening and dislocation strengthening. [ABSTRACT FROM AUTHOR]

We report on a study of the influence of microstructure on the mechanical behavior of bulk nanoporous Cu fabricated by chemical de-alloying of Cu 50 Al 50 , Cu 40 Al 60 , Cu 33 Al 67 and Cu 30 Al 70 (at%) alloys. The precursor Cu–Al alloys were fabricated using arc melting and bulk nanoporous Cu was obtained by subsequent de-alloying of Cu–Al alloys in 20 wt% NaOH aqueous solution at a temperature of 65 °C. We studied the microstructure of the precursor Cu–Al alloys, as well as that of the as de-alloyed bulk nanoporous Cu, using X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. Moreover, the compressive strength of bulk nanoporous Cu was measured and the relationship between microstructure and mechanical properties was studied. Our results show that the microstructure of bulk nanoporous Cu is characterized by bi-continuous interpenetrating ligament-channels with a ligament size of 130±20 nm (for Cu 50 Al 50 ), 170±20 nm (for Cu 40 Al 60 ) and 160±10 nm (for Cu 33 Al 67 ). Interestingly the microstructure of de-alloyed Cu 30 Al 70 is bimodal with nanopores (100's nm) and interspersed featureless regions a few microns in size. The compressive strength increased with decreasing volume fraction of porosity; as porosity increased 56.3±2% to 73.9±2%, the compressive strength decreased from 17.18±1 MPa to 2.71±0.5 MPa. [ABSTRACT FROM AUTHOR]