Thixoforming of SiC ceramic matrix composites in pseudo-semi-solid state

1INTRODUCTIONIt has great economic profit to exploit the uti-lization of SiC ceramic material for its strength,hardness,wear resistance,corrosion resistanceand high temperature resistance,abundant re-source and low price.But the brittle charactergreatly restricts its application in the field of engi-neering structure materials.Recently a series ofceramic matrix composites with exi mious perform-ance have been developed by reinforcing the matrixmaterial with other materials.Al/SiC is a la…     

Effect of Zr content on quench sensitivity of AlZnMgCu alloys

The effect of Zr content on quench sensitivity of AlZnMgCu alloys was investigated by mechanical properties testing and microstructure observations. The results show that with the increase of Zr the quench sensitivity relative to hardness and strength increases, while that relative to elongation decreases. From hardness and strength viewpoints, the low quench sensitivity is observed for the Zr-free and 0.05% Zr-containing alloys, which is quite quench sensitive from the ductility viewpoint. The largest quench sensitivity relative to hardness and strength is observed for 0.1% Zr-containing alloy, this is mainly due to large amount of high angle grain boundaries and incoherent Al3Zr dispersoids caused by recrystallization, which may efficiently promote heterogeneous precipitation during air quenching. More than 0.05% Zr can significantly decrease the quench sensitivity relative to ductility, which can be primarily attributed to recrystallization inhibiting and grain refining effects of Zr.     

Mechanism of strengthening of cube texture for high purity aluminum foils by additional-annealing

1　INTRODUCTIONHighpurityaluminumfoilsareusedastheanodematerialofhighvoltageelectrolyticcapacitorswhichneedstrongcubetexture { 0 0 1}〈10 0〉forlargeeffec tivesurfacefromchanneletching[1] .Becauseofitstechnicalimportance ,alotofeffortshavebeenmadetodevelopstrongcubetextureinhigh purityalu minumfoils[2 8] .Itwasfoundthatthecubetextureinthefoilscanbestrengthenedviaanannealingpro cessfollowedbyalowcoldrolling[7,8] ,andsuchanannealingiscalledadditional annealinginthispaper .Buttherewerefewinv…     

淬火速率对AlZnMgCu(Zr)合金断裂行为的影响

通过室温力学性能测试,光学显微镜、扫描电镜和透射电镜研究了淬火速率对AlZnMgCu(Zr)合金断裂行为的影响.结果表明:含Zr小于0.1%合金随着淬火速率的降低,由穿晶破断和沿晶开裂的混合型断裂逐渐转变成沿晶断裂;其主要原因是淬火速率降低使晶界无沉淀析出带(PFZ)宽化.含Zr大于等于0.1%的合金随着淬火速率的降低由穿晶破断为主的断裂逐渐转变成沿晶开裂和穿晶剪切的混合型断裂;沿晶断裂的产生主要是由于晶界无沉淀析出带宽化;穿晶剪切主要是由于慢速淬火过程中晶粒内部析出了大量粗大的η平衡相.     

固溶后预析出对7A55铝合金力学及腐蚀性能的影响

采用硬度测试、电导率测试及透射电镜观察，研究固溶后降温至440℃预析出处理时间对7A55铝合金板材力学和腐蚀性能的影响。结果表明：随预析出处理时间的延长，基体析出相逐渐增多且长大，导致合金时效后硬度和强度先提高而后降低；晶界析出相逐渐长大，晶界无沉淀析出带宽化，晶界相不连续性先提高而后降低，导致合金抗晶问腐蚀和剥落腐蚀性能也先升高而后降低。     

淬火介质对7055铝合金晶界析出行为的影响

采用透射电镜研究了淬火介质对7055铝合金晶界析出相及无沉淀析出带的影响。结果表明，空气淬火时，合金冷却过程在晶界上析出η平衡相。合金经室温水淬及沸水淬火合金时效后，晶界析出相尺寸差别小，呈链状连续分布；晶界无沉淀，析出带较窄，平均宽度分别约为33nm和43nm。空气淬火合金时效后晶界析出相尺寸差别较大，呈不连续分布；晶界无沉淀，析出带很宽，约102nm。对其原因进行了分析和讨论。     

Zn含量对Al-Zn-Mg-Cu合金挤压棒材耐剥落腐蚀性能的影响

通过剥落腐蚀浸泡实验和极化曲线测试,研究了Zn含量对Al-Zn-Mg-Cu合金挤压棒材耐剥落腐蚀性能的影响,结合金相显微镜、扫描电镜、扫描透射电镜等微观组织表征方法对影响机理进行了分析和讨论。结果表明:Zn含量(质量分数)由7.93%增至9.85%时,棒材剥落腐蚀抗力下降,剥落腐蚀等级由EA变成EC,最大腐蚀深度由334 μm增至579 μm。Zn含量增加,合金中粗大第二相数量增加,时效后晶界η相尺寸和间距变小、Zn和Mg含量增加,是耐剥落腐蚀性能下降的主要原因。     

2024铝合金航空座椅支承零件等温模锻成形研究

采用Deform-3D有限元软件及等温模锻试验对2024铝合金航空座椅支承零件的成形过程进行了模拟与试验研究,并且分别对等温模锻件和热轧板机加工零件的组织和性能进行了对比研究。结果表明,在420℃、锻压速度为1.5 mm·s-1、保压时间为1.5~2 min的锻造工艺参数条件下,2024铝合金航空座椅支承零件锻造成形的最大锻压力为12700 k N,锻件成形金属流动顺利。在本文的工艺条件下试制锻造了多件2024铝合金航空座椅支承件,测试分析结果表明,通过等温模锻制造的航空座椅支承零件较热轧板机加工零件强度提高11.4%,最高的强度为508 MPa,且不同方向力学性能的差异小于3%。     

非等温回归再时效对Al-8Zn-2Mg-2Cu合金厚板厚向组织及性能均匀性的影响

为进一步提升航空铝合金厚板的组织及性能均匀性,本文研究了升、降温回归及再时效对Al-8Zn-2Mg-2Cu合金厚板厚向组织及性能均匀性的影响.结果表明,在回归加热阶段,相对于板材心层,表层预析出相的回溶程度更高,但未回溶的η′或η相尺寸相对粗大.在回归后的缓慢冷却阶段,厚板的表层和心层都存在未溶第二相的缓慢粗化和新相的...     

复合能场铸轧对AZ61镁板组织及性能的影响

采用金相显微镜、扫描电镜、拉伸及弯曲性能测试等分析手段,研究复合能场(超声波和电磁场)铸轧工艺对AZ61镁合金板微观组织、力学性能和加工性能的影响。结果表明:与常规铸轧镁合金板带相比,复合能场可有效减小晶粒尺寸,并使析出相均匀弥散分布;施加复合能场之后,铸轧板抗拉强度、屈服强度及伸长率较常规铸轧板分别提高10.58%、12.84%和52.17%,而终轧成品板分别提高10.45%、20.56%和65.25%,且板材轧制后具有裂纹倾向小、抗弯强度及最大挠度大、弯曲抗力小等性质,可有效减少加工过程中材料及工具磨损,获得较好的综合性能。