关键词： Mg alloys   Stress corrosion cracking   Pre-exposure embrittlement   Gas-analysis   Slow-strain rate tensile testing   Quantitative fractography  

摘要： Pre-exposure of Mg alloys to corrosive media causes their embrittlement, which has been long associated with diffusible hydrogen penetrating into the metal. The time of the pre-exposure was suggested to promote embrittlement due to increasing both the corrosion damage and hydrogen concentration. However, recently it was shown that removal of corrosion products from the pre-exposed specimens results in full elimination of the all harmful effects induced by pre-exposure. This observation casts doubts about the significance of diffusible hydrogen in pre-exposure embrittlement. In view of those new findings, the effect of pre-exposure time on the embrittlement phenomenon is revisited in the present study. The specimens of the ZK60 and AZ31 alloys were pre-exposed to 4% NaCl + 4% K2Cr2O7 corrosive media for different durations and then slow-strain rate tensile tested in air either as are or after removal of corrosion products. It is found that the pre-exposure embrittlement of both alloys increases with the increasing pre-exposure time and is caused by the combined effect of the corrosion damage and the brittle cracking mechanism. The latter is (i) activated by the deposition of the essentially thick corrosion products layer on the specimen surface during pre-exposure, (ii) promoted by the increasing amount of corrosion products and (iii) can be fully inhibited by the removal of corrosion products from the specimen surface. The corrosion damage produces the irreversible loss in ductility and strength, which becomes more pronounced with the increasing pre-exposure time, but it does not alternate the fracture mode. No evidence is found for the increasing concentration of diffusible hydrogen in Mg alloys with the increasing preexposure time.

关键词： Magnesium alloy   Tension   compression asymmetry   Compression-extrusion   Microstructure   Texture  

摘要： Tension/compression symmetrical ZK61 magnesium alloy rod with fine grain and weak texture was achieved by compression-extrusion process. The formation mechanism of fine grain and weak texture was analyzed by investigating the microstructure and texture evolution during compression-extrusion process. In compression stage, {10-12} twinning deformation was activated greatly, which brought about significant grain refinement and formation of 0002 ||ED texture. As extrusion process going on, twinning gradually decreased and basal slip dominated the following deformation. Texture oriented into single annular shape by subsequent twinning in early extrusion and the annulation rotated toward ED gradually then merged into fiber texture by basal slip in late extrusion. Besides, texture was weakened by grain boundary slip and non-basal slip. With DRXed grain orientations similar to that of the deformed parent grains, Discontinuous dynamic recrystallization played a dominant role in grain refinement during extrusion stage, but the refinement was relatively minor compared to twining refinement in compression stage. Finally, magnesium alloy with fine grain and weak texture was achieved. The benefit of this microstructure and texture characteristic upon mechanical properties was the great enhancement of compressive yield strength, from the suppression of twinning when compressed. Therefore, tension/compression asymmetry was greatly improved by compression-extrusion process.

关键词： dissimilar material joining   carbon fiber reinforced polymer   AZ31B   friction self-piercing riveting   mechanical strength   corrosion performance   welding and joining  

摘要： In the present work, thermoset carbon fiber-reinforced polymer (CFRP) was spot joined to magnesium alloy AZ31B by a friction self-piercing riveting (F-SPR) process. Lap shear tensile and cross-tension testing were used to evaluate the mechanical joint performance. An average lap shear tensile load of 5.18 kN was achieved, while an average of 2.81 kN was found from cross-tension testing. All F-SPR samples showed a pullout of AZ31B after mechanical testing, indicating good mechanical interlocking between the steel rivet and AZ31B. Corrosion potential was measured for each material to establish the galvanic corrosion characteristics. As expected, AZ31B was found to be the most active, while thermoset CFRP was the most noble. The steel rivet fell between the AZ31B (active) and the thermoset CFRP (noble). Salt fog corrosion testing (ASTM B-117) was performed to evaluate the corrosion performance of the uncoated F-SPR joint. With up to 200 h of exposure, the post-corroded F-SPR joint integrity retained 81.2% of the pre-exposure F-SPR joint strength with AZ31B pullout failure mode. From cross-sectional analysis of the F-SPR joint, extensive corrosion of AZ31B was observed at the joint and other exposure areas. However, steel rivet was not significantly corroded due to sacrificial anode effect by which AZ31B corroded first in the galvanic couple.

关键词： 植入人工骨   椎体成型术   骨质疏松   骨折  

摘要： 目的:比较植入人工骨和椎体成型术治疗老年骨质疏松性骨折的临床效果。方法:选取2018年6月-2019年6月玉林市中西医结合骨科医院接诊的80例骨质疏松性骨折患者,采用交替分组法分为两组,实施不同手术方案,对照组40例行椎体成型术,试验组40例行植入人工骨手术,分析疗效。结果:术后1 d,两组骨代谢水平对比无统计学意义(P>0.05)。术后3个月,两组BALP水平对比差异无统计学意义(P>0.05);试验组BGP水平高于对照组(P<0.05)。术后3个月,试验组骨密度高于对照组(P<0.05)。试验组临床总有效率97.50%,高于对照组的85.00%(P<0.05)。试验组骨折愈合时间(16.01±1.12)周,较对照组短(P<0.05)。试验组术后6 h疼痛评分低于对照组(P<0.05)。试验组术后3、6、12个月疼痛再次发生率低于对照组(P<0.05)。结论:与椎体成型术治疗对比,植入人工骨治疗老年骨质疏松性骨折疗效更加显著,有助于缩短骨折愈合时间,促进骨折恢复,对于骨代谢具有一定积极意义。

关键词： AZ80镁合金   热扭转变形   动态再结晶   微观织构  

摘要： 利用Gleeble-3500热模拟试验机对AZ80镁合金进行了热扭转变形试验,变形温度分别选取为300、340和380℃,扭转角速度为0.7 rad/s。利用光学显微镜(OM)和电子背散射衍射技术(EBSD)对AZ80镁合金在扭转变形条件下的显微组织和微观织构演变规律进行了研究。结果表明:热扭转变形能够显著细化晶粒,当扭转角速度一定时,升高温度能够促进动态再结晶(DRX)的产生,提高变形组织的均匀性。同时,小角度晶界所占比例随着变形温度的升高而逐渐减小,表明有连续性动态再结晶(CDRX)的发生。此外,热扭转变形能够显著调整合金的微观织构,织构极密度随着温度的升高呈现出先降低而后升高的趋势,在340℃时取得最小值18.476。

关键词： 机械合金化   可降解金属   Fe 30 Mn x Ca合金   腐蚀速率   生物相容性  

摘要： 通过机械合金化、粉末压坯及热挤压的方法制备了医用可降解Fe_(30)Mn_(x)Ca(x=0,1.5,3.0,4.5)合金棒材,运用金相显微镜、SEM、拉伸测试、电化学测试和SBF浸泡腐蚀等研究了Ca的添加对合金组织及性能的影响.结果发现,Fe_(30)Mn_(x)Ca合金均由奥氏体组成,且随着Ca质量分数增加,该合金硬度增加,伸长率和强度降低,降解性能显著提高,腐蚀速率从Fe 30 Mn的0.1130 mg/(cm^(2)·d)增至Fe_(30)Mn_(4.5)Ca的0.2260 mg/(cm^(2)·d).细胞毒性实验表明其生物相容性为0~1级.

关键词： 镁合金   机械合金化   热压烧结  

摘要： 以Mg粉、Sn粉和Zn粉为初始原料,采用机械合金化和热压烧结的方法制备Mg-25Sn-x Zn合金。研究了Zn添加量对Mg-25Sn合金显微组织和性能的影响。结果表明:Mg-25Sn-x Zn体系的机械合金化过程中,Zn元素不参与合金化反应,但Zn的引入降低了Mg+Mg2Sn混合物的尺寸。除固溶外,烧结态Mg-25Sn-x Zn中Zn完全转变成MgZn2相。且随Zn含量的增加,MgZn2相的尺寸逐步增大,Mg晶界和Mg2Sn颗粒相周围是MgZn2相的择优分布位置。添加6%Zn(质量分数)的Mg-25Sn合金具有最优的力学性能,其显微维氏硬度为1.60GPa、屈服强度为388MPa、抗压强度为497 MPa、断裂应变7.5%。

关键词： AZ91D镁合金   激光选区熔化   固溶处理   时效处理   显微组织   耐腐蚀性  

摘要： 目的研究热处理对激光选区熔化成形(Selective Laser Melting,SLM)AZ91D镁合金组织与耐蚀性能的影响。方法利用SLM技术成形了AZ91D镁合金,对试样进行固溶处理(T4)、固溶+时效处理(T6)。采用金相显微镜、扫描电镜、X射线衍射仪、电化学工作站分别对SLM、T4热处理、T6热处理的AZ91D镁合金试样的微观组织和耐蚀性能进行观察与测试。结果SLM试样经420℃保温6 h固溶处理后,β-Mg17Al12相基本固溶于基体中,晶粒尺寸由5μm增大至60μm左右。加热至200℃保温2 h时效处理后,β-Mg17Al12相从基体析出,随着时效时间由2 h增加至6 h,析出相数量逐渐增多。在3.5%NaCl溶液中浸泡120 h后,SLM试样表面腐蚀坑较小;T4热处理试样表面出现较大的腐蚀坑;T6热处理试样的表面腐蚀坑大小及深浅不一,腐蚀最严重。极化曲线结果表明,SLM试样的腐蚀电流密度Jcorr最小,为(1.889±0.2)×10^(–5)A/cm^(2),耐蚀性能最好;固溶+时效处理2 h的试样Jcorr最大,为(1.225±0.2)×10^(–4)A/cm^(2),耐蚀性能最差。不同热处理试样的耐蚀性能优劣排序为:SLM试样>T4试样>T6试样。结论未经热处理的SLM试样晶粒尺寸最小,耐蚀性最好。经420℃保温6 h固溶处理后,β-Mg17Al12相基本溶解,晶粒尺寸增大1个数量级;加热至200℃时效2 h处理后,耐蚀性最差,当时效时间继续延长至6 h后,β-Mg17Al12相的数量逐渐增多,耐蚀性能反而有所增强。

关键词： 稀土元素Y   铸造AZ81镁合金   微观组织   力学性能  

摘要： 稀土元素对镁合金铸造性能的影响与添加的稀土元素含量有直接关系。本文研究了不同含量的Y元素对AZ81镁合金组织中晶粒和第二相结构的分布规律。采用拉伸试验研究了铸造AZ81镁合金试样在室温和170℃的力学性能。结果表明,元素Y的加入可以有效细化铸造AZ81镁合金的晶粒组织,且细化效果随着Y元素含量的增加而逐渐加强。当Y元素含量达到1.5%时,细化效果达到最大。随着稀土元素Y的加入,AZ81镁合金的室温和高温(170℃)强度都获得了明显的提升,且屈服强度和抗拉强度随Y含量的增高均呈现出了先增加后降低的趋势,当Y的含量为1.5%时达到最大。

关键词： 高纯镁   镁-1钙合金   细胞活力   肌肉植入   生物相容性  

摘要： 目的探讨高纯镁和镁-1钙合金2种镁基材料的体内外生物相容性,为其临床应用提供安全性数据。方法选择高纯镁和镁-1钙合金2种镁基材料,参照ISO 10993系列标准,开展细胞毒性、遗传毒性、皮内反应、致敏性、急性全身毒性和26w肌肉植入后组织反应的研究,探讨细胞活力的影响因素,评价其生物相容性。结果高纯镁和镁-1钙合金的细胞存活率分别为(70.5±5.7)%和(54.1±3.8)%,调节pH值为7.4后,2种材料的细胞存活率均有所增加。高纯镁和镁-1钙合金均未诱发鼠伤寒沙门氏菌的体外基因回复突变、未引起体外哺乳动物细胞L5178Y TK^+/-的TK基因突变和染色体诱变、未引起小鼠急性全身毒性反应、皮肤过敏和皮内反应;植入后26 w对局部肌肉组织均无明显的刺激作用。结论在本试验条件下,高纯镁的细胞存活率优于镁-1钙合金,Mg^2+的释放不是影响其细胞活力的单一因素,在一定的Mg^2+浓度范围内,细胞活力可能更依赖于其酸碱环境;2种镁基材料无遗传毒性、无急性全身毒性、无刺激性和致敏性,具有良好的组织相容性。