SiC颗粒增强AZ81镁合金基复合材料

采用熔体搅拌法制备SiC颗粒增强AZ81镁合金基复合材料,并对其摩擦磨损性能进行研究。应用熔体搅拌法制备的SiCp/AZ81镁合金基复合材料具有SiC颗粒分布均匀、与基体结合紧密的特点;10μmSiCp/AZ81复合材料的抗拉性能较好,且加入SiC颗粒可使AZ81镁合金复合材料的耐磨性提高15.4%～18.3%。

原位CuYSi颗粒增强块体镁基非晶合金复合材料的研究

用Mg-4%Si合金、纯Cu、纯Mg、Cu-38%Y合金经普通铜模铸造方法制备了一种原位颗粒增强Mg60Cu30Y10块体非晶合金复合材料。运用XRD以及EDS确定其颗粒为CuYSi相,采用SEM-EDS对颗粒的形貌、大小及成分进行了分析,并对Mg60Cu30Y10块体非晶合金复合材料的硬度及热稳定性进行了研究。结果表明,原位生成的CuYSi颗粒尺寸细小(10μm左右),形状规整并且均匀分布在非晶合金基体上;与Mg60Cu30Y10块体非晶合金相比,CuYSi颗粒的生成使得非晶合金复合材料的硬度增加102.5HV,ΔTx增加6.1K。

浸渍—挤压(SiC_w+B_4C_p)/Mg(AZ91)复合材料的微观组织

利用透射电子显微术研究了浸渍挤压 (SiCw+B4Cp) /Mg(AZ91)复合材料的微观组织结构。结果表明 ,B4Cp/Mg界面处生成了很多MgO和MgB2 反应产物 ,而SiC/Mg界面处反应产物较少。基体中形成了大颗粒体心立方结构的Mg17(Al,Zn) 12 相和未知的弥散小颗粒物相。大量观察及综合分析表明 ,SiC和Mg之间不存在固定晶体学位向关系 ,只可能出现一些择优取向关系 ,出现几率较大的取向关系为 :{ 111} SiC∥ { 0 0 0 1} Mg,〈1—0 1〉SiC∥〈112 —0〉Mg和 { 111} SiC∥ { 10 1—0 } Mg,〈11—0〉SiC∥〈12 —10〉Mg。

氧化的碳化硅与铝镁合金之间的界面反应

通过 ＦＥ－ＳＥＭ（ｆｉｅｌｄ ｅｍｉｓｓｉｏｎ－ｓｃａｎｎｉｎｇ ｅｌｅｃｔｒｏｎ ｍｉｃｒｏｓｃｏｐｙ），ＴＥＭ（ｔｒａｎｓｍｉｓｓｉｏｎ ｅｌｅｃｔｒｏｎ ｍｉｃｒｏｓｃｏｐｙ）和Ｘ射线衍射研究了高温氧化的ＳｉＣ颗粒增强含镁铝合金基复合材料的界面反应过程．发现该界面反应首先形成纳米ＭｇＯ，然后是否继续与铝液反应取决于Ｍｇ的含量以及纳米ＭｇＯ层致密程度．在Ｍｇ含量不足以形成致密的纳米ＭｇＯ层时，ＳｉＯ２与ＭｇＯ和铝液继续反应形成ＭｇＡｌ２Ｏ４晶体；当Ｍｇ的含量足以形成致密的纳米ＭｇＯ层，则其能良好地保护内层ＳｉＣ免受铝液的进一步侵蚀．表明ＭｇＯ和ＭｇＡｌ２Ｏ４均为高温热稳定界面反应产物．澄清了对于该界面反应过程的模糊认识和推测．这对于复合材料界面反应控制及界面设计具有重要价值．

Hot extrusion of SiC_p/AZ91 Mg matrix composites

SiC particles reinforced AZ91 Mg matrix composites （SiCp/AZ91） with SiC volume fractions of 5%, 10% and 15% were fabricated by stir casting. After T4 treatment, these composites were extruded at 350 °C with an extrusion ratio of 12：1. In the as-cast composite, particles segregated at a microscopic scale within the intergranular regions. Hot extrusion almost eliminated this particle aggregation and improved the particle distribution of the composites. In addition, extrusion refined the grains of matrix. The results show that hot extrusion significantly improves the mechanical properties of the composites. In the as-extruded composite, with the increase of SiCp contents, the grain size of the extruded composites decreases, the strength and elastic modulus increase but the elongation decreases.

Fabrication of carbon nanotubes reinforced AZ91D composites by ultrasonic processing

Magnesium matrix nanocomposite reinforced with carbon nanotubes(CNTs/AZ91D) was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing.The microstructures and mechanical properties of the nanocomposite were investigated.The results show that CNTs are well dispersed in the matrix and combined with the matrix very well.As compared with AZ91D magnesium alloy matrix,the tensile strength,yield strength and elongation of the 1.5%CNTs/AZ91D nanocomposite are improved by 22%,21%and 42%respectively in permanent mold casting.The strength and ductility of the nanocomposite are improved simultaneously.The tensile fracture analysis shows that the damage mechanism of nanocomposite is still brittle fracture.But the CNTs can prevent the local crack propagation to some extent.

Effect of Mg-based spherical quasicrystal on microstructures and mechanical properties of ZA54 alloy

To improve the strength, toughness and heat-resistance of magnesium alloy, the microstrucmre and mechanical properties of ZA54 alloy reinforced by icosahedral quasicrystal phase （/-phase） particles were studied. Except α-Mg, φ-phase and τ-phase, MgZnYMn I-phase particles can be obtained in ZA54-based composites by the addition of icosahedral quasicrystal-contained Mg-Zn-Y-Mn master alloy. The introduction of MgZnYMn I-phase into ZA54 alloy has great contribution to the refinement of matrix microstructures and the improvement of mechanical properties. When the addition of Mg-based spherical quasicrystal master alloy is up to 3.5% （mass fraction）, the macro-hardness of ZA54-based composites is increased to HB 68. The impact toughness of composites reaches the peak value of 18.3 J/cm^2, which is about 29% higher than that of ZA54 mother alloy. The highest tensile properties at ambient and elevated temperatures with master alloy addition of 2.5% （473 K） are also obtained in ZA54-based composites with 3.5% （mass fraction） Mg-Zn-Y-Mn master alloy addition. The ultimate tensile strength of composites at ambient and elevated temperatures are 192.5 MPa and 174 MPa, which are 23.4% and 33.8% higher than that of ZA54 mother alloy, respectively. The improved mechanical properties are mainly attributed to the pinning effect of I-phase on grain boundaries.

Interaction between AE44 magnesium alloy and SiC-Al_2O_3-SiO_2 ceramic foam

The interaction between a molten magnesium alloy AE44 and a SiC?Al2O3?SiO2 ceramics and the resulting reaction products were studied. The samples were investigated using optical and electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. SiO2was predominantly reduced by Mg during the contact of the magnesium-rich melt with the ceramics. The main reaction product was MgO, whilst Si dissolved in the melt. Two novel tetragonal phases formed at the interface: AlSiRE and AlMgSiRE, having a specific mutual crystallographic orientation relationship. The interactions resulted in strongly connected interfaces between the metal and ceramics after short interaction time; however, interactions lead to disintegration of the ceramics after longer contact time.

Effect of nano-sized Al2O3 reinforcing particles on uniaxial and high cycle fatigue behaviors of hot-forged AZ31B magnesium alloy

The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31 B alloy and AZ31 B/1.5 vol.%Al2 O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 ℃ and then an open-die forging at 450 ℃. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain;however, a degradation was observed in the high applied strain region. Unlike AZ31 B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.

High specific strength MWCNTs/Mg-14Li-1Al composite prepared by electrophoretic deposition, friction stir processing and cold rolling

Multi-wall carbon nanotubes reinforced Mg-14Li-1Al composite(MWCNTs/Mg-14Li-1Al) was prepared by the processes of electrophoretic deposition, friction stir processing, and cold rolling. The microstructure and mechanical properties of the composite were investigated. The results show that, the microhardness of the composite is up to HV 84.4, which is 91.38% higher than that of the as-cast matrix alloy(HV 44.1). The yield strength and ultimate tensile strength of the composite are 259 and 313 MPa, which are 135.45% and 115.86% higher than those of the as-cast matrix alloy, respectively, and a high specific strength of 221.98 k N·m/kg is obtained. In the composite, the MWCNTs serve as nucleation particles during the friction stir processing and cold rolling, causing dynamic recrystallization and grain refinement. Furthermore, MWCNTs hinder the movement of dislocations and transfer the load from the matrix alloy, thus improving the strength.