Effect of Cr content and cooling rate on the primary phase of Al-2.5Mn alloy

The effect of Cr content and cooling rate on the microstructure of Al-Mn alloy was studied using well resistance furnace melting,and the alloy was analyzed using scanning electron microscopy(SEM)and X-ray diffraction(XRD).The experimental results showed that adding Cr could significantly improve the morphology of the primary phase in the Al-2.5Mn alloy.Without Cr,the primary phase in the alloy was thick,needle-like,and strip-like structure.After adding 0.2wt%-0.5wt%Cr,the primary phase in the upper part of the alloy was gradually fined and reached the best effect at 0.35wt%Cr.When the content of Cr was 0.5wt%,the microstructure of the primary phase in the upper part began to coarsen.The bottom of the alloy was a large bulk phase,but still much finer than that without adding Cr.XRD and SEM analysis showed that the precipitation phase at the bottom was mainly Al85Mn7Cr8,while the fine microstructure at the top was Al6Mn and Al3Mn.The results of the cooling rate experiments showed that the primary phase of Al-2.5Mn-0.35Cr was further refined,and the eutectic microstructure was partly achieved,under air-cooling condition.And when the cooling method was iron die-cooling,the microstructure of the Al-2.5Mn-0.35Cr alloy was changed into a eutectic microstructure.

Effects of La-Ce addition on microstructure and mechanical properties of Al-18Si-4Cu-0.5Mg alloy

The microstructural evolution and mechanical properties of Al-18 Si-4 Cu-0.5 Mg alloy modified by the addition of La-Ce rare earth elements through OM,SEM,EPMA and tensile tests were investigated.The results of OM and SEM analyses indicated that primary Si particles were significantly refined from coarse block-like and irregular polygonal shapes into fine flaky shapes,while eutectic Si particles were modified from coarse and needle-like into fine and rod-or coral-like shapes with increase of La-Ce addition.The alloy exhibited the minimum primary Si particle size and the best mechanical properties with the addition of 0.3 wt.%La-Ce.The average particle size decreased from 61 to 28 μm,the ultimate tensile strength increased from 222 to 242 MPa and the elongation increased from 3.2% to 6.3%.In addition,modification mechanisms and fracture modes were explored by the means of SEM and EPMA.

Effect of heat treatment processing on microstructure and tensile properties of Ti-6Al-4V-10Nb alloy

Effects of heat treatment processing on the microstructure and mechanical properties of Ti-6Al-4V-10Nb alloy were investigated. The microstructures were investigated by SEM, TEM and XRD, and the mechanical properties were evaluated by tensile tests at room and elevated temperatures. The results indicate that the lath-like and globular primary α phase, secondary α phase and β phase are obtained after forging and heat treatment processing. The size of secondary α phase is much smaller than that of primary α phase. After heat treatment, the volume fraction of primary α phase is decreased, and that of secondary α phase is increased. With the increase of solution temperature, the volume fraction of primary α phase is gradually decreased, and that of secondary α phase is obviously increased. The yield strength and tensile strength of Ti-6Al-4V-10Nb alloy are significantly enhanced with the solution temperature increasing.

Effect of Salvia Miltiorrhiza on Left Ventricular Hypertrophy and Cardiac Aldosterone in Spontaneously Hypertensive Rats

Chronic treatment with Salvia Miltiorrhiza preventing left ventricular hypertrophy (L VH) and its possible mechanism- inhibiting the action of cardiac aldosterone in spontaneously hypertensive rats (SHR) were investigated.Normotensive Wistar- kyoto (WKY ) rats and SHRs were used.Part of SHRs was treated with Salvia Miltiorrhiza for 12 weeks.Systolic blood pres- sure (SBP) and left ventricular mass index were measured.Sections of heart tissue were stained with HE method and Van Gieson method.Collagen volume fraction was determined in the leftven- tricle by automatically quantitative m orphometry.Cardiac aldosterone concentration was measured by radioimm unoassay.The results indicated thatcom pared with WKY rats,SHRs exhibited high- er SBP,left ventricular collagen volume fraction,and aldosterone concentration (all P<0 .0 5 ) . After the treatm ent with Salvia Miltiorrhiza,SBP,left ventricular collagen volum e fraction,and aldosterone concentration in SHR were decreased as compared with control group (P<0 .0 5 ) ex- cept SBP.It was concluded thatchronic treatment with Salvia Miltiorrhiza could preventleftven- tricular hypertrophy in SHR,significantly inhibit collagen compositions in left ventricle.The m echanism was probably related with the inhibition of the cardiac aldosterone action.

Effect of holding time on microstructure and mechanical properties of Al-40 wt.%Si alloys fabricated by combination of gas atomization and spark plasma sintering

Hypereutectic Al-40 wt.%Si alloys were fabricated by the combination of gas atomization and spark plasma sintering(SPS) technology. The effects of holding time(15-60 min) on phase composition, microstructure, density,mechanical properties of Al-Si alloys were investigated by XRD, SEM, a hydrostatic balance, an automatic micro hardness tester and a universal tensile testing machine. The results showed that homogenous distribution of ultrafine primary Si and high density of alloys can be obtained at holding time of 30 min. Compared with primary Si(3.7 μm)fabricated by gas atomization, the average size increased from 5.17 to 7.72 μm with the increase of holding time during SPS process. Overall, the relative density, maximum tensile strength and Vickers hardness of 94.9%, 205 MPa and HV;196.86 were achieved at holding time of 30 min, respectively. In addition, all the diffraction peaks were corresponded to α-Al or β-Si and no other phase can be detected. Finally, the densification process of SPS was also discussed.

Effect of abruptly changing withdrawal rate on solidification microstructure in directionally solidified Al-4.5wt%Cu alloy

Al-4.5wt.%Cu alloy has been directionally solidified at constant and abruptly changing withdrawal rates, respectively. The effects of the withdrawal rate on solidification microstructure, primary dendrite arm spacing(PDAS) and liquid solute distribution in front of the solid-liquid interface were investigated. The experimental results for the PDAS at a constant withdrawal rate agree well with the values calculated by the Hunt, Trivedi and Hunt-Lu models. At an abrupt change in the withdrawal rate, the maximum to minimum ratio of the PDAS at a given solidification parameter, i.e. λ1max/λ1min, is more than 2, and the PDAS values are remarkably history-dependent. Further, the liquid-solute distribution curve based on theoretical calculation shows that the larger the initial withdrawal rate is, the smaller the minimum of liquid solute concentration in front of the solid-liquid interface is after the abrupt change in withdrawal rate.

特发性醛固酮增多症临床实践新进展

原发性醛固酮增多症(primary aldosteronism,PA)是继发性高血压最常见的发病原因之一,未能得到正确诊疗的PA可能导致严重的心血管疾病和肾脏毒性反应。临床医生应对高风险人群进行PA检测及分型诊断以确定治疗方案。单侧肾上腺切除术及使用盐皮质激素受体拮抗剂的终身药物治疗法分别是针对单侧及双侧病变的有效治疗方案。特发性醛固酮增多症(idiopathic hyperaldosteronism,IHA)是临床上PA最常见的亚型,肾上腺静脉取样(adrenal vein sampling,AVS)是PA分型诊断的金标准,但其在临床应用过程中具有诸多局限性。本文综述了IHA病因及诊疗的最新研究进展,为IHA患者的临床诊治提供新思路。

ACTHR在介导血管紧张素Ⅱ和氯化钾对醛固酮分泌调控中的实验研究

目的研究血管紧张素Ⅱ（AT-Ⅱ）和氯化钾刺激人肾上腺皮质癌H295R细胞后醛固酮合成酶（CYP11B2）mRNA及醛固酮激素的改变情况，并探讨促肾上腺皮质激素受体（ACTHR）在介导该反应中的作用。方法用慢病毒包装的ACTHR高表达载体感染H295R细胞作为实验组。空载体病毒转染组细胞为对照组。应用免疫印迹Westernblot和荧光定量PCR法验证ACTHR表达情况。分别用100nmol／LAT-Ⅱ及16mmol／L氯化钾刺激各组细胞，刺激24h后测定CYPllB2mRNA表达水平，对比2组细胞CYP11B2mRNA增幅情况。用ELISA试剂盒测定醛固酮激素的含量，对比2组细胞醛固酮增幅情况。结果实验组细胞ACTHR在蛋白水平和mRNA水平分别增加2．4倍和18倍（P〈0．05）。AT-Ⅱ刺激24h后实验组细胞CYP11B2 mRNA表达水平较对照组细胞高1．7倍，2组细胞醛固酮激素水平分别为（121．98±8．31）ng／L和（104．05±6．88）ng／L，前者增幅为后者的2．06倍（—P〈0．05）；氯化钾刺激各组细胞24h后，实验组细胞CYP11B2mRNA表达水平较对照组细胞高19．2倍，2组细胞醛固酮激素水平分别为（137．67±10．35）ng／L和（104．05±6．88）ng／L，前者增幅为后者的3．13倍（P〈0．05）。结论ACTHR高表达可增加醛固酮对AT-Ⅱ和氯化钾刺激的敏感性，有望成为研究原发性醛固酮增多症重要突破口。