铝合金中Mg2Si相的时效析出过程

描述了Al-Mg-Si/Al-Si-Mg系合金时效析出的一般序列为α-sss→GP区→β″→β′→β(Mg2Si),总结了在析出序列中可能出现的各亚稳相的晶体结构模型,讨论了各阶段析出相的形成或转变过程及其强化作用;并就过量的Si、Cu、大塑性变形等对析出相的影响作了探讨。

Modification and refinement mechanism of Mg_2Si phase in Sr-containing AZ61-0.7Si magnesium alloy

The effect of Sr on modification and refinement of the Mg 2 Si phase in an AZ61-0.7Si magnesium alloy has been investigated and analyzed.The results indicate that Sr can effectively modify and refine the Chinese-script shaped Mg2Si phase in the AZ61-0.7Si alloy.By adding 0.06wt.%-0.12wt.%Sr to AZ61-0.7Si alloy,the Mg2Si phase in the alloy can be changed from the initial coarse Chinese-script shape to fine granule and/or irregular polygonal shapes.Accordingly,the Sr-containing AZ61-0.7Si alloy exhibits higher tensile and creep properties than the AZ61-0.7Si alloy without Sr modification.The mechanism on modification and refinement of the Mg2Si phase in Sr-containing AZ61-0.7Si alloy is possibly related to the following two aspects:(1)adding Sr may form the Al4Sr phase which can serve as the heterogeneous nucleus for the Mg2Si particles and/or(2)adding Sr may lower the onset crystallizing temperature and increase the undercooling level.

Modification and refinement effects of Sb and Sr on Mg_(17)Al_(12) and Mg_2Si phases in Mg-12Al-0.7Si alloy

The effects of Sb and Sr on the modification and refinement of Mg17Al12 and Mg2Si phases in Mg- 12Al-0.7Si alloy were investigated and compared. The microstructure and mechanical properties of Mg-12Al0.7Si alloy and its modification mechanism by Sb and Sr were investigated using a scanning electron microscope （SEM）, an energy dispersive spectrometer （EDS）, X-ray diffraction （XRD） and differential thermal analysis （DTA）. The results indicate that by adding 0.5wt.% Sb to the Mg-12Al-0.7Si alloy, the Mg17Al12 phase was refined and broken into some discontinuous island structures. However, some network Mg17Al12 phases still can be detected in Mg-12Al-0.7Si-0.09Sr alloy. Therefore, Sb performs better in modification and refinement of Mg17Al12 phase than does Sr. Small amounts of fine polygonal shaped Mg2Si phases were found in Mg-12AI-0.7Si-0.5Sb alloy, while the morphology of Mg2Si phases in Mg-12Al-0.7Si-0.09Sr alloy changed from the coarse Chinese script shapes to fine granule and irregular polygonal shapes, indicating that the effects of modification and refinement on Mg2Si phase are more significant by adding 0.09wt.% Sr than 0.5wt.% Sb. The ultimate tensile strengths of the Sb and Sr modified Mg-12Al-0.7Si alloys were considerably increased both at room temperature and at 200 ℃.

Cr变质对汽车驱动轴用Mg2Si/Al-Fe基复合材料组织和性能的影响

以Al-Fe合金为原材料,通过Mg-Si熔体直接反应制备Mg_2Si/Al-Fe基复合材料,研究Cr变质对复合材料组织中初始Mg2Si和富Fe相变质行为,以及拉伸性能和耐磨性的影响。结果表明：组织中生成了树枝晶Mg2Si相,针形相,以及共晶Si相与α（Al）相。通过Cr变质处理后,针形的β-Fe相转变为了骨骼形的α-Fe相,并且初生的Mg2Si相外形也变得更加规则,初生Mg2Si相尺寸减小31%。Cr变质处理后,复合材料的拉伸强度增加幅度达到14.8%,磨损性能增强了1.5倍,伸长率增加了50%。采用Cr变质处理后,试样拉伸断口部位生成了部分韧窝结构,出现了塑性断裂特征。

Ce对铸造Mg-5Al-2Si合金中Mg2Si相改性及力学性能的影响

利用X射线衍射、光学显微镜和扫描电镜等分析测试手段,研究了不同Ce添加量对重力铸造Mg-5Al-2Si合金显微组织和力学性能的影响规律。结果表明,添加Ce以后,合金中主要存在α-Mg相、汉字状Mg2Si相、多边形Mg2Si相、细小的Al11Ce3和CeSi2相;稀土Ce的加入改变了合金中Mg2Si相的尺寸、形貌与分布;随着Ce含量增加,汉字状Mg2Si相的平均长度大幅度减小,共晶Mg2Si相的形貌由粗大的汉字状转变为多边形状;当Ce添加量为0.4%时,试验合金的力学性能达到最佳,而增加至0.8%时,合金的力学性能反而下降。拉伸断口形貌也揭示了合金的力学性能情况。因此,适当的Ce添加量(0.4%)可以有效地改性Mg2Si相,从而提高合金的强度和伸长率。

变质元素对Mg/Mg2Si复合材料中Mg2Si相影响的研究进展

Mg2Si相作为一种具有良好性能的二元合金相,被广泛地应用在多种有色合金以及复合材料中作为增强相。采用不同的元素得到了不同的变质效果,通过变质元素细化Mg2Si相,以提高合金的性能。研究了不同元素对Mg/Mg2Si复合材料中的Mg2Si相的复合变质作用。综述了Mg2Si相的性质,重点介绍了铸造镁合金中添加变质元素对Mg2Si相形貌的影响以及变质机理,总结了当前研究阶段存在的不足,并提出了进一步研究方向。

Comparison of Sb and Sr on modification and refinement of Mg_2Si phase in AZ61-0.7Si magnesium alloy

The effects of Sb and Sr on the modification and refinement of Mg2Si phase in an AZ61-0.7Si magnesium alloy were investigated and compared. The results indicate that the difference of Sb and Sr in the modification and refinement of Mg2Si phase is significant. Addition of 0.4%Sb(mass fraction) to AZ61-0.7Si alloy can refine but not modify Mg2Si phase. Oppositely,by addition of 0.12%Sr to AZ61-0.7Si alloy,the Mg2Si phase changes from initial coarse Chinese script shape to fine granule and/or irregular polygonal shape. Accordingly,the Sr-modified AZ61-0.7Si alloy exhibits higher tensile and creep properties than the Sb-modified one. The difference of Sb and Sr in the modification and refinement of Mg2Si phase is possibly related to the following two aspects:1) the disregistry at(100)Al4Sr//(100)Mg2Si is lower than that at(0001)Mg3Sb2//(111)Mg2Si(0.69% vs 1.72%) and 2) the onset crystallizing temperature of the Sr-modified AZ61-0.7Si alloy is lower than that of the Sb-modified one(603.1 ℃ vs 606.9 ℃).

Thermal stability of Mg_2 Si epitaxial film formed on Si(111) substrate by solid phase reaction

A single crystalline Mg2Si film was formed by solid phase reaction （SPR） of a Si（111） substrate with an Mg overlayer capped with an oxide layer（s）,which was enhanced by post annealing from room temperature to 100℃ in a molecular beam epitaxy （MBE） system.The thermal stability of the Mg2Si film was then systematically investigated by post annealing in an oxygen-radical ambient at 300℃,450℃ and 650℃,respectively.The Mg2Si film stayed stable until the annealing temperature reached 450℃ then it transformed into amorphous MgOx attributed to the decomposition of Mg2Si and the oxidization of dissociated Mg.

Effects of magnesium content on phase constituents of Al-Mg-Si-Cu alloys

By means of scanning electron microscopy(SEM), energy dispersive spectrum(EDS), X-ray diffractometry(XRD) and metallographic analysis, the effects of variation of magnesium content on phase constituents of Al-Mg-Si-Cu alloys were investigated. The results indicate that the constituents formed during casting alloys are main Al1.9CuMg4.1Si3.3,Al4(MnFe)3Si2 and Mg2Si, while pure Si is only present in the alloy containing lower magnesium content. Increasing Mg content leads to increasing the amount of Mg2Si, but decreasing the amount of Al1.9CuMg4.1Si3.3 and Al4(MnFe)3Si2. During the following homogenization process, Al1.9CuMg4.1Si3.3 is completely dissolved, Al4(MnFe)3Si2 and pure Si remain unchanged. After rolling and final heat treatment, the constituents in the alloys change no longer.

Tensile Properties and Wear Resistance of Mg Alloy Containing High Si as Implant Materials

Magnesium alloy has been considered as one of the third-generation biomaterials for the regeneration and support of functional bone tissue.As a regeneration implant material with great potential applications,in-situ Mg_(2)Si phase reinforced Mg-6Zn cast alloy was comprehensively studied and expected to possess excellent mechanical properties via the refining and modifying of Mg_(2)Si reinforcements.The present study demonstrates that the primary and eutectic Mg_(2)Si phase can be greatly modified by the yttrium(Y)addition.The size of the primary Mg_(2)Si phases can be reduced to~20μm with an addition of 0.5 wt.%Y.This phenomenon is mainly attributed to the poisoning effect of the Y element.Moreover,wear resistance and tensile properties of the ternary alloy have also been improved by the Y addition.Mg-6Zn-4Si-0.5Y alloy exhibits optimal tensile properties and wears resistance.The ultimate tensile strength and the elongation of the alloy with 0.5 wt.%Y are 50%and 65%higher than those of the ternary alloy,respectively.Excessive Y addition(1.0 wt.%)deteriorates the tensile properties of Mg-Zn-Si alloy.The improvement of the tensile properties is mainly due to the modification of primary and eutectic Mg_(2)Si phases as well as the solid solution strengthening of the Y atoms.This study provides a certain implication for the application of Mg-Zn-Si alloys containing Y elements as regeneration implants.

Effects of isothermal process parameters on semisolid microstructure of Mg-8%Al-1%Si alloy

A Mg-8%Al-1%Si alloy with semisolid microstructure was fabricated by isothermal heat treatment process. The effects of isothermal process parameters such as holding temperature and holding time on the microstructure of Mg-8%Al-1%Si alloy were investigated. The results show that a non-dendritic microstructure could be obtained by isothermal heat treatment. With increasing holding temperature from 560 to 575 °C or holding time from 5 to 30 min, the liquid volume fraction increases, the average size of α-Mg grains grows larger and globular tendency becomes more obvious. In addition, the Mg2Si phase transforms from Chinese script shape to granule shape. The morphology modification mechanisium of Mg2Si phase in Mg-8%Al-1%Si alloy during the semisolid isothermal heat treatment was also studied.

Sr和Sb变质AZ61-0．7Si合金的铸态组织和力学性能

Mg2Si相的变质和细化被认为是改善含Si镁合金力学性能的关键因素之一。研究了Sr和Sb变质AZ61-0.7Si镁合金的铸态组织和力学性能。研究结果表明:添加0.4%(质量分数)Sb对AZ61-0.7Si镁合金中的汉字状Mg2Si相有一定细化作用,但没有明显变质效果。相反,添加微量Sr对AZ61-0.7Si合金中的汉字状Mg2Si相有明显变质和细化作用。在AZ61-0.7Si合金中添加0.03%～0.09%Sr(质量分数)后,合金中的Mg2Si相从粗大汉字状形貌变为细小的颗粒状和/或多边形状。相应地,合金的抗拉性能和蠕变性能得到显著提高。

合金元素对Mg-Al-Si系镁合金中Mg_2Si相形貌影响的研究进展

合金化和微合金化作为变质Mg-A1-Si系镁合金中汉字状Mg2Si相的一种工艺手段,目前已引起国内外的广泛关注和高度重视,并对此开展了大量的研究。本文综述了合金元素变质Mg-Al-Si系耐热镁合金中汉字状Mg2Si相的研究进展,尤其是Al、Si、Sb、Ca、P、RE和Sr等合金元素对汉字状Mg2Si相形貌的影响及其变质机理,指出了目前还存在的问题,并对今后的发展进行了展望。

Sb对原位Mg_2Si/Al-5Si复合材料显微组织的影响

研究了Sb含量对Mg2Si/Al-5Si复合材料显微组织的影响。结果表明,随着Sb含量的增加,初生Mg2Si颗粒形貌明显发生了细化,Mg2Si形态由变质前的汉字体和枝晶状变为细小的、均匀分布的颗粒状,Mg2Si体积分数也有所增加。当Sb含量为0·4%时,细化效果达到最佳,由变质前的52μm变为25μm。当Sb含量超过0·4%后,Mg2Si颗粒尺寸开始粗化,因此,过量的Sb对Mg2Si颗粒的细化无益。Sb对Mg2Si颗粒的细化主要由于AlSb引起的异质形核作用,Sb使液相线温度和熔体表面张力σLV降低,对Mg2Si颗粒的细化也具有一定的作用。

Sb变质对Mg-6A1-1Zn-0.7Si镁合金热处理组织和力学性能的影响

通过金相、扫描电镜(SEM)、X射线衍射分析(XRD)和差热分析(DSC)等手段,研究Sb变质对Mg-6Al-1Zn-0.7Si镁合金热处理组织和力学性能的影响,尤其是对合金固溶处理组织的影响。结果表明:固溶处理可以变质Mg-6Al-1Zn-0.7Si镁合金铸态组织中的汉字状Mg2Si相,使Mg2Si相从汉字状变为短杆状和条块状,并且添加0.4%Sb到实验合金中可使固溶处理变质汉字状Mg2Si相的效果提高。也正是由于固溶处理可以使实验合金组织中的汉字状Mg2Si相变质,使得Mg-6A1-1Zn-0.7Si合金时效处理后获得了较铸态更高的的抗拉性能和抗蠕变性能,并且添加0.4%Sb可以进一步增强热处理对性能的改善作用。

Sb变质Mg-6Al-1Zn-0.7Si镁合金的组织和性能

研究了Sb变质Mg-6Al-1Zn-0.7Si镁合金的凝固行为、铸态组织及力学性能。研究结果表明:Mg-6Al-1Zn-0.7Si合金的铸态组织主要由初生!-Mg、M17Al12和Mg2Si相组成,其中Mg2Si相的汉字状形态非常明显,且比较粗大。而添加0.4%Sb变质后,合金组织中的Mg2Si相变得相对细小,从而使合金的拉伸性能以及抗蠕变性能得到提高。此外,添加0.4%Sb对Mg-6Al-1Zn-0.7Si合金凝固过程中的相变类型没有影响,并且对合金的相变峰值温度、开始转变温度和凝固温度范围的影响也不大。

Sr对过共晶Mg-Si合金中初生Mg_2Si相变质的影响

利用Mg-20%Sr中间合金对过共晶Mg-Si合金进行变质处理,对比研究了碱土元素Sr加入量对Mg2Si初晶变质效果(主要包括形态和尺寸)的影响规律,并讨论其变质机制。研究结果表明:碱土元素Sr对过共晶Mg-Si合金中的Mg2Si初晶可有效变质。随着Sr含量的增加,Mg2Si初晶的平均尺寸和尺寸分布范围均逐渐降低,其形态由粗大树枝状晶、细小树枝晶、非规则外形颗粒到规则外形颗粒逐渐过渡。当Sr含量达到2.0%,此时Mg2Si初晶主要呈现为规则外形,平均尺寸为50μm左右。其变质机理应主要与碱土元素富集于Mg2Si相生长表面并抑制优先生长晶向的生长有关。

ECAP变形对Mg_2Si增强耐热镁合金组织及性能的影响

为了提高镁合金的耐热性能,在Mg-Zn合金中加入Si,形成Mg-Zn-Si镁合金.采用ECAP工艺在变形温度为573 K和挤压路径为Bc条件下对Mg-Zn-Si镁合金进行不同道次的变形.运用金相显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等手段对变形后的Mg-Zn-Si镁合金进行了组织表征,对变形后的合金进行了室温拉伸和高温蠕变等力学性能测试.结果表明:随着挤压道次增加,α-Mg基体、Mg Zn相及Mg2Si相均得到细化且分布趋于均匀.1道次挤压后部分基体α-Mg细化,4道次挤压后α-Mg的尺寸减小为5~10μm,且晶粒大小趋于均匀;2道次挤压后Mg2Si相枝晶在原位置破碎为颗粒状,6、8道次挤压后Mg_2Si相呈弥散分布.4道次挤压后合金的屈服强度和抗拉强度均提高120%,伸长率提高353%;8道次挤压后合金的抗拉强度和伸长率与4道次相比变化不大,但屈服强度进一步提高了19%.随着挤压道次增加,高温抗蠕变性能提高,8道次后高温稳态蠕变速率降低5倍.Mg2Si相细化机理为受剪切而机械碎断.

Al_2O_(3f)/Mg-9Al-0.5Nd复合材料的组织与压缩性能

采用无压浸渗技术制备了Al2O3f/Mg-9Al-0.5Nd复合材料,利用扫描镜、X射线衍射仪、电脑伺服材料试验机,研究了复合材料的微观组织变化、压缩性能和断口形貌。结果表明,复合材料组织中出现了Mg2Si新相和少量的粒状和杆状稀土相;热处理后Mg2Si有增多的趋势,尺寸略有增大;复合材料经过T4和T6处理后压缩强度有所下降,由铸态的346.5MPa下降到250.5MPa和327.5MPa;经T6处理后,复合材料的压缩断裂方式由准解理断裂变为混合断裂,存在少量纤维从基体中拔出的现象。

往复挤压制备Mg_2Si/Mg-Al复合材料组织及时效行为研究

对用石墨型铸造方法制备的Mg2Si/Mg-Al基复合材料进行了多道次往复挤压及时效处理,以探讨该材料组织与硬度的变化规律。结果表明:Mg2Si/Mg-Al复合材料经往复挤压7道次后,Mg2Si相分布均匀且小于30μm,基体晶粒尺寸<10μm,复合材料硬度为150.7HV,与铸态相比提高了22.5%;挤压后的材料经215℃时效6h后,硬度为163.9HV,较铸态提高了33.3%。硬度的提高得益于基体组织、Mg2Si和Mg17Al12的细化,而时效后硬度进一步提高是由于固溶到基体中的Al原子以颗粒状Mg17Al12相析出。