Strength of casting high entropy alloys (HEAs) improved by the introduction of ceramic particle. However, the strengthening process of alloys were hindered by the problem of particle agglomeration seriously. In this paper, the ultrasonic vibration (UV) treatment process was introduced to improve the dispersion of ceramic particles. Al0.4CoCrFe2Ni2 HEAs contain different particle sizes TiC were successfully prepared. Morphology of TiC (mu m) change from long straight rod to network structure with UV treatment, and the average dendrite spacing decreases. TiC (nm) particles were dispersed uniformly and agglomeration decreased remarkably. The mean free path (L) of dislocation motion is increased greatly. Additionally, a new substructure region formed by introducing ceramic phase TiC. Dislocation density increased around substructure region after UV, the energy and driving force provided by UV for the overturning of substructure region to sub-grains. Ultimate tensile strength of UV-Al0.4-TiC (nm) alloy reaches 572 MPa under the action of the second phase, Hall-Petch strengthening and other mechanisms, and the fracture elongation as high as 49.6 %. Compared with the non-ultrasonic alloy, the yield strength is increased by 10 %, and elongation after fracture is increased by 41.3 %. Compared with Al0.4 matrix alloy, the yield strength is increased by 92.8 %. Therefore, the influence of UV assisted treatment on particle reinforced alloys with different sizes was analyzed in this paper. UV assisted treatment proved to provide an effective method to solve the agglomeration of reinforced particles and offer a novel pathway to design cast HEAs with an exceptional amalgamation of strength and ductility.

In order to improve the wear resistance of austenitic ductileiron (ADI), varying amounts (0, 0.25, 0.5 and 0.75 wt 207_ - 7^ + 12 HV5), ultimate tensile strength ( 452_ - 9^ + 7 MPa) and elongation (14.4

The carbon fibers-diamond (50 vol%)/ Al composite (CFs-D/Al) was successfully designed and fabricated using gas pressure infiltration. By comparing it to the carbon fiber/Al composite (CFs/Al), a dual reinforcement structure with both soft and hard materials was formed, resulting in improved anisotropy. This improvement can be attributed to the high hardness of diamond (D), which bears most of the pressure during infiltration. The thermal conductivity (TC) of the CFs-D/Al in the XY plane and Z direction were measured to be 249.97 W center dot m- 1 center dot K- 1 and 225.81 W center dot m- 1 center dot K- 1, respectively. These values represent a 27.24% and 133.2% increase in TC compared to CFs/Al. The improved anisotropy, excellent TC of diamond, high density, and good interface are the main factors contributing to this enhancement in thermal conductivity. Additionally, CFs-D/Al demonstrated acceptable coefficients of thermal expansion (CTEs) of 7.26 x 10-6 K-1 (in the XY plane) and 10.04 x 10-6 K-1 (along the Z direction). This is mainly attributed to the low CTE of carbon fibers and diamond, as well as the presence of good interfacial pinning and residual stress in the composite. Furthermore, the addition of carbon fibers greatly reduced the wear of cutting tools compared to D/Al. The surface roughness of the CFs-D/Al after machining was measured to be 5.939 mu m, which is 51.86% and 70.97% lower than that of CFs/Al and D/Al, respectively. This reduction in surface roughness can be attributed to the lubricating effect of CFs and the ability of D to prevent peel pits under the adhesive wear mechanism. This research utilized the design concept of combining the advantages of different reinforcements to surpass the limitations of using a single reinforcement for heat dissipation purposes.

In order to improve the mechanical properties of ductile iron, different contents of SiO2 particles are added into ductile iron in the casting process. The microstructure and mechanical properties of ductile iron are studied. It is found that SiO2 particles can promote the heterogeneous nucleation of austenite, which can indirectly promote the nucleation of graphite, ferrite and cementite. SiO2 particles can also inhibit the growth of austenite, which can further refine ferrite and cementite during the phase transformation. Finally, the average grain size of ferrite decreased to 27.95 μm and the interlamellar spacing of pearlite decreased to 211 nm in sample 0.5S. A large number of granular pearlite appeared in sample 0.75S. The above changes of microstructure affect together the properties of ductile iron, so that the strength, plasticity and toughness were enhanced simultaneously. Ductile iron has the best tensile strength (495 MPa), elongation (26.1

High entropy alloys (HEAs) with single FCC structure exhibits unique structure and properties. However, lack of strength hinds the engineering application ability seriously. Therefore, it is urgent to propose effective methods and theories to enhance the strength while maintaining favorable plasticity. Introducing reinforced phases is one crucial research approach for improving the mechanical properties of HEAs. However, the resulting reduction in ductility has been neglected. In this work, we propose a novel multi-scale TiC coupling reinforced alloy which preserves the high plasticity while increasing the strength. The results demonstrate that TiC (mu m) hinders the dislocations movement and improves strength through the second phase strengthening mechanism. Apart from acting as barriers to dislocation motion, the TiC (nm) also provides more dislocation sources in the distortion area at the junction with the matrix, which increasing the number of movable dislocations and enhancing the plastic strain capacity. Compared with the Al0.4 alloy, the tensile yield strength of the Al0.4-TiC (mu m + nm) alloy is increased by 145 %, the ultimate tensile strength is up to 574 MPa, while maintaining a high plastic strain by 30.1 %. The addition of multi-scale ceramic phase TiC provides a novel approach to obtain high strength and high plasticity HEAs.

T8 treatment includes solution treatment, cold working and artificial aging treatment. T8 treatment can greatly improve the hardness and strength of 2024 aluminum alloy without reducing the corrosion resistance. The effect of 0, 1, 2, 3, and 4% cold-drawing deformation on the microstructures of the alloy was observed by transmission electron microscopy, and properties of the alloy was investigated by hardness tests, tensile tests and electrochemical corrosion tests. The results show that the mechanical properties and corrosion resistance of cold-drawing deformed 2024 aluminum alloy are better than those of non-deformed alloy. Compared with AA2024-T6, AA2024-T8 with 2% cold-drawing deformation has a higher hardness by 11.3%, and a higher tensile strength by 10.8%. The improvement of the properties of AA2024-T8 is mainly due to the interaction between dislocations and precipitates. With the increase in cold-drawing deformation, the nucleation points of precipitates in AA2024-T8 gradually increase, and precipitates are gradually coarsened under the same artificial aging treatment.

To improve the application of molten salt method in carbon fibers (CFs) surface modification, the work explores the effect of the CFs-itself crystallinity on the formation and growth mechanism of TiC coating in the molten salt reaction. Three different types of CFs were used to prepare TiC coatings at 850°C, and the formation and growth mechanisms were studied. The results showed that CFs surface defects could preferentially initiate nucleation and cause inhomogeneity of TiC particles in the initial stage of TiC coating formation. The CFs surface with high crystallinity could obtain a finer and more uniform TiC coating because the growth rate of TiC particles is slower and the particles do not accumulate with each other during the coating growth. At the same time, the growth rate of TiC coating decreased with increasing CFs crystallinity during the TiC coating growth, which reason is that CFs with higher crystallinity require more activation energies of carbon atom counter diffusion. Therefore, the surface of CFs with higher crystallinity and fewer surface defects is easier to obtain a uniform and particle size TiC coating during the molten salt reaction.

The contradiction between strength and ductility limits the application of high-entropy alloys (HEAs). To simultaneously improve the strength and ductility of HEAs, the cryogenic treatment was proposed and applied in this paper. The Al0.6CrFe2Ni2 HEA with dual-phase structure was selected as the experimental material for cryogenic treatment. The microstructure and mechanical properties of the HEA in an as-cast and cryogenically treated state were analyzed in detail. The results showed that the grain size of equiaxed crystal in the alloy decreased continuously by prolonging the cryogenic treatment time, and the average value was 44.6 μm for the cryogenically treated HEA at the time of 48 h, which was 46.5% lower than that of the as-cast alloy. The number and size of ordered body-centered cubic (B2) spherical nanophases embedded in the body-centered cubic (BCC) structured inter-dendritic region, however, increased continuously by extending the cryogenic treatment time. The cryogenic treatment also made more slip systems activate, cross-slip occurred in the alloy, and a large number of stacking faults were found in the transmission electron microscopy (TEM) microstructure for the alloy that underwent a long time in cryogenic treatment. The yield strength of the Al0.6CrFe2Ni2 HEA was gradually increased with the increase in cryogenic treatment time, and the maximum yield strength of the 48 h cryogenically treated alloy was 390 MPa, which was 39.3% higher than that of the as-cast. This increase in mechanical properties after cryogenic treatment was attributed to the refinement of grains and the large precipitation of nanophases, as well as the appearance of cross-slips and stacking faults caused by cryogenic treatment.

In order to improve the wear resistance of ductile iron, different contents of TiC particles are added into ductile iron used lost-foam casting and the tribological behavior of ductile iron is studied through a ball-on-disk sliding test. It is found that with the increase of TiC content, the pearlite content gradually increases, which is attributed to TiC promoting the heterogeneous nucleation of cementite and increasing cooling rate of the melt. The increase of pearlite content and the second-phase strengthening caused by TiC improve the hardness and tensile strength of ductile iron. Ductile iron has the best tensile strength (498 MPa) and hardness (168 HV1) with a TiC content of 1 wt.%. The wear resistance also increases with increasing TiC content. The wear volume is reduced from 0.14 to 0.03 mm3, and the main wear mechanism changes from adhesive wear to abrasive wear. The oxide layer produced by frictional heat on the worn surface and the hardened layer produced by strain hardening on the subsurface further improve the wear resistance. Therefore, the wear resistance of ductile iron is affected by the changes of microstructure before and after wear.

采用回归再时效处理2024铝合金并对其进行透射电镜和扫描电镜观察、硬度、晶间腐蚀和电化学腐蚀测量,研究了回归时间对2024铝合金的微观组织和耐蚀性能的影响.结果表明:经回归再时效处理的2024铝合金其主要析出强化相为S相.回归处理时间为0.2 h的合金,S相细小且呈弥散均匀分布,性能有显著的提高,硬度为147.2 HV0.5、晶间腐蚀深度为98.5 μm、自腐蚀电位为-0.64 V、自腐蚀电流密度为0.24 μA·cm-2、电阻值为31397 Ω·cm2.这表明,适当时间的回归处理有利于提高2024铝合金的硬度和耐蚀性.

To simultaneously improve the mechanical properties and corrosion resistance of AA2024 aluminum alloy, a T8I4 with deep cryogenic treatment (DCT) process is proposed, which includes solution heat-treatment, cold-drawing deformation, pre-aging, DCT and re-aging. The microstructure of AA2024 is observed by confocal laser scanning microscope, scanning electron microscopy and transmission electron microscopy. The properties of AA2024 are studied by hardness measurement, tensile test, friction and wear test, ex-foliation corrosion test, intergranular corrosion test and electrochemical corrosion test. On comparison with T6, AA2024-T8I4 +DCT obviously increases its hardness, tensile strength and wear resistance. AA2024-T8I4 +DCT has similar corrosion resistance to T7X two-stage aging. According to comprehensive analysis, the MPts in AA2024-T8I4 +DCT with 3 % deformation amount have the maximum pinning force to the dislocations, and the alloy has the largest hardness, strength and the best wear resistance. The dis-continuous grain boundary precipitates in AA2024-T8I4 +DCT with 1 % deformation amount are dis-continuous and fine, and the precipitate free zone is not obvious, which makes the corrosion difficult to develop. The alloy has the shallowest intergranular corrosion depth, the smallest corrosion rate and the best corrosion resistance (c) 2023 Elsevier B.V. All rights reserved.

This paper proposes a combined treatment of secondary aging (T6I4) and deep cryogenic treatment (DCT), which includes initial aging, DCT, and re-aging, to improve the limitations of secondary aging (T6I4) treatment on enhancing the mechanical properties of AA2024. The scanning electron microscopy and transmission electron microscopy (TEM) are used to observe the alloy's microstructure, and hardness measurements, tensile tests, friction and wear tests, intergranular corrosion tests, and electrochemical corrosion tests are used to determine the alloy's properties. On comparison with T6I4, AA2024-T6I4 with DCT for 1 h increases its hardness, tensile strength and wear resistance, as well as its corrosion resistance. A TEM analysis of AA2024-T6I4 with DCT for 1 h reveals uniform distribution of fine matrix precipitates, a small size difference, and discontinuous and fine grain boundary precipitates within the alloy.

In order to improve the overall properties of cast Al–Cu–Mn alloy, the effect of Zr content on the microstructure and corrosion resistance of Al–Cu–Mn alloy was investigated. The microstructures of the alloy were analyzed by scanning electron microscopy and transmission electron microscopy, and the corrosion resistance of the alloy was tested by exfoliation corrosion (EXCO), intergranular corrosion (IGC) and electrochemical corrosion tests. The results show that the corrosion resistance of Al–Cu–Mn alloy with 0.2 wt

To improve the antioxidation of Cu-coated carbon fibers (Cf), the Sn coating was prepared on the surface of the Cu-coated Cf by electroless plating, and then the Cu-Sn coating was compounded by heat treatment with different temperatures in this study. Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), and weighing methods were used to investigate the relationship between the surface topography, phase transformation, and antioxidation of Cu-Sn composite coating and heat treatment temperature. The results show that Cu-Sn composite coating after heat treatment has significant antioxidation compared with Cu coating due to the development of intermetallic compounds. As the heat treatment temperature rises, the antioxidation of the composite coating rises as well. The Cu-Sn composite coating has the best antioxidation when the heat treatment temperature is 973 K. Because the outer Cu3Sn of the heat-treated coating avoids direct contact between the Cu coating and oxygen during the oxidation process, the antioxidation ability is proportional to the fraction of Cu3Sn phase in the coating. This study has a significant impact on improving the application of Cu-coated Cf in metal matrix composites.

7xxx系铝合金作为高强度铝合金的代表,以其较高的强度以及良好的韧性和耐蚀性等优异性能而广泛地应用于航空航天及交通运输领域.该类可热处理强化铝合金对微观组织结构敏感,其性能受合金内部析出相的形核、生长及分布情况的影响.采用三级时效工艺—回归再时效处理,通过预时效、回归、再时效3个过程的有效配合改变合金的析出相状态,可以达到合金力学性能和耐蚀性能的良好结合.目前已有大量针对其在7xxx系铝合金应用的研究,并取得了一定进展.文中介绍了回归再时效处理的方法,以及其对7xxx系铝合金微观组织的改变和合金性能的影响,同时对目前该领域的研究现状进行归纳总结.

7075 alloy was treated with deep cryogenic treatment (DCT) and retrogression and re-aging treatment (RRA). The corrosion behavior of the alloy was investigated by potentiodynamic polarization measurement, electrochemical impedance spectroscopy and intergranular corrosion test. The microstructure and corrosion morphology of the alloy were observed by transmission electron microscope and scanning electron microscope, respectively. The results showed that DCT could change the electrochemical corrosion process of the alloy. DCT applied to different stages of RRA treatment had a great influence on the number, size and distribution of the matrix and grain boundary precipitates. When DCT was applied after retrogression treatment, Icorr and corrosion rate of the alloy on electrochemical test was 0.006 mA cm-2 and 0.197 mm/a, respectively, and IGC depth was 25 mu m. Moreover, the discontinuous grain boundary precipitates showed a better distribution state, thus corrosion resistance was remarkably improved.

Al 0.4 CoCrFe 2 Ni 2 high-entropy alloys with different additions of TiO 2 nano-ceramic particles (0, 1.25vol.%, 2.5vol.%, 3.75vol.% and 5vol.%, respectively) were prepared by using the vacuum arc melting method. The effects of TiO 2 addition on the crystal structure, microstructures and mechanical properties of the alloy were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and tensile testing. The microstructure analysis shows that the TiO 2 nano-ceramic particles added in the alloy are decomposed, and a small amount of Al 2 O 3 and a great number of intermetallic compounds (γ′ phases) with simple cube structure are formed. The γ′ phases are enriched at inter-dendrite, which increases the resistance of dislocation movement during the deformation of the alloy, thus balancing the problem of high plasticity and low strength of the alloy. When the addition of TiO 2 is 2.5vol.%, the strength of the high-entropy alloy reaches the maximum of 489 MPa, which is 11.1% higher than the matrix alloy composed of single FCC phase.

为探究和改善7xxx系铝合金耐腐蚀性能,采用电化学分析和透射电镜观察等手段,针对7075铝合金回归再时效(RRA)处理过程中的不同回归程度进行电化学腐蚀行为研究.结果表明:较为充分的回归处理有利于基体析出相回溶,经再时效处理后基体析出相细小弥散,有利于钝化膜的修补;晶界析出相粗大且断开分布,阻断腐蚀通道,延缓腐蚀的进行;较为明显的晶间无析出带,更大程度地减缓了基体与晶界析出相之间的电位差,缓解合金的腐蚀敏感性.RRA处理后的合金电化学腐蚀抗性均优于峰值时效处理的,经过120℃预时效20 h、190℃回归15 min、120℃再时效20 h处理的样品在电化学腐蚀过程中自腐蚀电位、自腐蚀电流密度和腐蚀速率分别为?1.12 V、3.4μA/cm2和为0.11 mm/a,电化学腐蚀抗性得到显著改善.

The good mechanical properties of aluminum alloys can be obtained by the retrogression and re-aging (RRA) treatment. The microstructure of Al-Cu-Mg alloy after each stage of RRA treatment was observed by transmission electron microscopy (TEM), the mechanical properties of the alloy was studied by hardness tests and the wear resistance was studied by reciprocating friction tests. The results show that the hardness of Al-Cu-Mg alloy after pre-aging at 190 °C for 2 h, retrogression at 320 °C for 0.2 h and re-aging at 190 °C for 8 h reaches the peak, which is 148.6 HV, and the wear resistance is the best. The strengthening phases of Al-Cu-Mg alloy after RRA treatment mainly are S phases. When the pre-aging is in the under-aging state, it is beneficial to redissolve S phases into the alloy during the retrogression. An appropriate retrogression time is beneficial to the formation of more and fine S phases after RRA treatment.

A recently developed AA7075 was subjected to solid solution, high temperature laser surface treatment and artificial aging. The microstructure evolution and precipitation behavior were examined, and their effects on corrosion behavior and corrosion cracking were analyzed. The results show that the coarse η phase disappears and many smaller η phases are formed after high temperature laser surface treatment. Most of the phases dissolved into Al matrix during solution, and fine η phases precipitated in laser treatment. The η′ phases were appeared in the high temperature laser surface treatment samples. It was concluded that reasonable laser scanning power owned the best corrosion resistance, lower intergranular corrosion tendency. Both lower laser scan power and higher scan power samples were susceptible to the intergranular corrosion, and the intergranular cracking was observed. In contrary, the reasonable sample which the laser power is 1000 W showed much better corrosion resistance due to the coarsening and separation of grain boundary precipitations.