Corrosion influence on surface appearance and microstructure of compo cast ZA27/SiC_p composites in sodium chloride solution

The influence of corrosion on the surface appearance and microstructure of particulate ZA27/SiCp composites was examined after 30 d immersion in a sodium chloride solution with the access of atmospheric oxygen. The composites with different contents of SiC micro-particles were synthesized via compo casting. Microstructural studies by means of optical microscopy （OM） and scanning electron microscopy （SEM） showed that corrosion occurred in the composite matrices, preferentially in regions of the η phase, rich in zinc. The corrosion processes did not affect the silicon carbide particles incorporated in the matrix alloy. According to the results of electrochemical polarization measurements, an increase in the content of SiC particles in the composite matrice has led to the lower corrosion resistance in the composites.

Sip/ZA27复合材料的晶粒细化工艺的研究

本文研究了Zr、RE对Sip/ZA27复合材料的晶粒细化工艺,结果表明:添加适当含量的Zr或RE时,都能使复合材料的晶粒得到一定程度的细化,Zr的晶粒细化能力强于RE,而只有Zr和RE复合添加才能得到细小的等轴晶组织,在添加0.2%Zr+0.8%RE时晶粒尺寸最小,达到60μm左右。

Aging microstructural characteristics of ZA-27 alloy and SiC_p/ZA-27 composite

The aging characteristics of as-quenched microstructures of ZA-27 alloy and SiCp/ZA-27 composite(ZMCp) were investigated using SEM, EDS and TEM. The structure, morphology and size of sub-grains in primary dendrite in ZMCp continuously change during aging process. Little tiny spherical Zn-rich η phase distributes in the dendrite. Amount of transitional α′phase, well coherent with equilibrium αf phase, in SiCp-neighboring dendrite edge zone is less than that in dendrite center zone. Both eutectic and peritectic β phase transform into lamellar α and η phases, obeying [ 2113]η∥[110]α, and (002)α∥ (1 101)η. In the like-eutecticum of ZMCp, less amount of β phase and decomposition products are found. The size of α phase decomposed from peritectic β phase in ZMCp is obviously larger than that in the monolithic alloy. The lamella decomposition of β phase beside SiCp is evidently more rapid than that in the alloy. SiC particulates strongly accelerate neighboring β phase decomposition in aging process.

Processing technique and sliding friction and wear behavior of TiB_2/ZA27 composite

In-situ TiB2 particles reinforced ZA27 composite was prepared by the stir-casting technique and a two-step method. TiB2/Al composite was produced by incorporating K2TiF6, KBF4 salts and other agents into Al melt. As a master alloy, TiB2/Al composite was used to manufacture TiB2/ZA27 composite, which results in the generation of well-distributed reinforcing TiB2 phase. The hardness, friction and wear behavior of TiB2/ZA27 composite were investigated. The results show that the hardness of the composite is enhanced with increasing the content of TiB2 particles, the incorporation of TiB2 reduces the wear rate of TiB2/ZA27 composite and improves the friction property under lubricated and dry sliding friction conditions. The worn track width of ZA27 alloy is 1.6 and 2.5 times as long as that of （2.1%）TiB2/ZA27 composite at 150N and 700N load under lubricated conditions, which indicates that TiB2/ZA27 composite possesses higher bearing ability.

SOLIDIFICATION MICROSTRUCTURE AND FRACTURE MORPHOLOGY OF SiCp/ZA27 COMPOSITE

Solidification microstructure and mechanical property are explored.Furthermore,tensile fracture and microstructure are analyzed by using SEM and JXA 840A electron probe.The results indicate that SiC particles in SiCp/ZA27 composite are mainly distributed on interfaces or between dendrites and surrounded by primary α phase.The dendrite of α phase is fined by SiCp.The tensile strength at room temperature decreases with the increasing of SiCp addition.The tensile strength at elevated temperature increases with the addition of SiCp.The fracture of SiCp/ZA27 composites is the mixture of tough and brittle fracture.The carck is prone to extend along the interface and the region of dispersed shrinkage.

原位自生Si_p/ZA27复合材料的磨损性能

研究Sip体积分数和实验温度对原位自生Sip/ZA27复合材料磨损性能的影响。结果表明:随着Sip体积分数的增加,其耐磨性呈先增大、后减小、进而又增大的趋势;随着实验温度的升高,复合材料的耐磨性减弱,但不同Sip体积分数的材料其耐磨性减小的幅度不同;所有这些变化均由磨损机理决定;随Sip体积分数的增加,材料的主导磨损机制将从较严重的磨损机制――塑性变形诱导磨损和粘着磨损转向轻微的磨损机制――涂抹磨损,进而又转向严重的磨损机制――塑性变形诱导磨损,最后则又转变为相对轻微的磨损机制――伴随磨料磨损的涂抹;随着实验温度的升高,主导磨损机制从轻微的磨损机制――伴随磨料磨损的涂抹转向严重的磨损机制――塑性变形诱导磨损和粘着磨损;高硬度磨层的形成与否决定着Sip/ZA27复合材料的耐磨性及磨损机制。

K_2O·6TiO_(2(w))/ZA-27复合材料显微组织与性能

采用挤压铸造法制备了Ｋ２Ｏ·６ＴｉＯ２晶须增强ＺＡ－２７合金复合材料，分析了复合材料的显微组织特性，利用ＴＥＭ对该复合材料界面的微观结构进行了观察与分析，测试了复合材料的抗拉强度和硬度。实验结果表明：该复合材料渗透完全，晶须分布均匀，观察有两种形态界面存在，复合材料的硬度随晶须含量的增加而显著提高。

原位自生Si_p/ZA27复合材料的制备及其力学性能

研究了原位自生硅颗粒(Si)p增强ZA27基复合材料的铸造法制备工艺以及该材料的力学性能。结果发现:硅含量一定,随浇注温度的降低Sip变大;浇注温度一定,随硅含量的增加Sip也变大。在适宜的浇注温度(750℃)和硅含量(体积分数10%)下,可得到初生硅颗粒形状规则、尺寸细小、分布均匀的Sip/ZA27。硅的加入使材料中形成了大量的缩松,导致力学性能的严重下降。初生硅颗粒的尺寸、形貌对Sip/ZA27的力学性能也产生影响。P变质效果明显,可以提高Sip/ZA27复合材料的力学性能。

预处理SiC颗粒在ZA-27合金中的分散润湿过程和界面反应模型

用扫描电镜 ( SEM)和透射电镜 ( TEM)并应用搅熔铸造工艺研究了预处理过的 Si C颗粒在加镁 ZA-2 7合金中的卷入、分散和润湿过程。在低温搅拌 ( 4 70℃ )时 ,预处理过的 Si C颗粒首先呈较大尺寸团聚体被卷入 ZA-2 7合金半固态浆料中 ,随后在搅拌剪切力的作用下 Si C团聚体逐渐变小 ,且由于发生了存在于 Si C表面的 Si O2与由于加 Mg而降低表面能的合金液间的润湿 ,并在旋涡能的促进下 ,Si C能呈单粒状分散在熔体中 ;在高温( 5 5 0℃ )搅拌时 ,由于 Si O2 与合金液中的活性原子 Mg和 Al等发生界面反应 ,促进了 Si O2 与合金液间的进一步润湿 ,随后 Si C能与合金液发生非反应润湿的主要原因是界面反应提供了无气洁净的 Si C表面。结合电镜观察和热力学计算及动力学分析 ,确认界面反应产物是尖晶石。探讨了搅拌时界面反应的过程并建立了反应润湿的模型 ,得出 Si C表面的残余 Si O2 厚度 X与反应时间 t成线性关系 ,即

K_2O·6TiO_(2(w))/ZA-27 合金复合材料高温磨损性能

通过ＳｑｕｅｅｚｅＣａｓｔｉｎｇ工艺制备了钛酸钾（Ｋ２Ｏ·６ＴｉＯ２）晶须增强锌铝合金（ＺＡ２７）复合材料，分析了Ｋ２Ｏ·６ＴｉＯ２（ｗ）／ＺＡ２７合金复合材料的微观组织特性，研究该复合材料及基体合金室温及高温（～１５０℃）摩擦磨损性能．实验结果表明：在边界润滑条件下，复合材料的高温耐磨性能比基体合金有显著提高；利用ＳＥＭ５０５扫描电镜对两种材料的磨损表面微观形貌进行了观察，并讨论了高温磨损失效机制．

Si_p/ZA27复合材料在部分重熔过程中的组织演变

研究了经Zr-P双重变质的Sip/ZA27复合材料在半固态温度475℃部分重熔过程中的组织演变。结果表明,经双重变质的复合材料,组织由发达的树枝晶变为短粗枝晶,初生Si变细小。在加热过程中,短粗枝晶粗化形成少晶界或无晶界的相连组织;随后因共晶组织的熔化造成组织分离,形成相互独立的不规则颗粒;最后由于不规则组织突出部位的熔化,使组织圆整化。在加热初期Si无明显的变化,随着加热时间的延长,Si棱角变得圆整,且有减小的趋势。

RE对Si_p/ZA27复合材料凝固组织的影响

研究了RE对Sip/ZA27复合材料的铸态、固溶态及半固态组织的影响,分析了随RE含量的变化复合材料组织形态的变化及RE的分布变化情况,并探究了RE对组织的影响机理。结果表明,随着RE含量的增加,晶粒形态由发达的羽毛状晶逐渐转变为等轴晶形态,晶粒尺寸呈减小趋势,在0.8%RE时晶粒尺寸最小;过量的RE与其他元素形成长针状的复杂化合物,使得细化作用减弱。

模具温度对Si_p/ZA27复合材料组织及性能的影响

研究了模具温度对触变成形Sip/ZA27复合材料组织及力学性能的影响。结果表明,随着模具温度升高,锭料的凝固速率变慢,初生α-Al颗粒尺寸和体积分数增大;而且初生α-Al颗粒中Zn元素的含量增加;此外,Si颗粒的团聚倾向变得严重。通过对试样的力学性能进行比较可知,最佳的模具温度为200℃,此时的抗拉强度和伸长率分别达到382 MPa和1.17%。而且随着模具温度的增加,断裂机制发生转变。