Zn对挤压态Mg-3Sn-1Ca合金耐蚀性的影响

目的 提高挤压态Mg-3Sn-1Ca合金的耐腐蚀性能。方法 通过合金熔炼制备了Mg-3Sn-Ca(TX31)和Mg-3Sn-Ca-Zn(TXZ311)两种挤压态合金,利用XRD、金相、SEM、EDS、EBSD、析氢、电化学极化曲线和阻抗谱,分析了TX31和TXZ311两种合金的微观组织及耐腐蚀性能。结果 XRD和EDS结果表明,挤压态TX31和TXZ311两种合金中第二相均为CaMgSn相,TXZ311合金中由于Zn的添加,CaMgSn相增加且分布更加均匀。金相和EBSD结果表明,Zn的添加可以提高TX31合金的动态再结晶程度和{0002}基面织构强度,改善TX31合金中组织的不均匀性。从极化曲线上可得,腐蚀电位和腐蚀电流分别为-1.57V和6.95×10^(-5)A。添加Zn后,腐蚀电位升高(-1.49 V),腐蚀电流减小(1.02×10^(-5)A),表明合金耐蚀性提高。对比两种合金阻抗谱可发现,TXZ311合金具有比TX31合金更大的容抗弧,表明其表面的电荷转移电阻和表面膜的电阻最高,动态腐蚀过程中氧化产物膜具有较好的稳定性,有效阻碍了α-Mg基体的腐蚀。TX31合金析氢量和时间成正比,腐蚀速率为3.7mm/a。而TXZ311合金腐蚀速率仅为1.6mm/a,析氢量在腐蚀12 h后明显降低,表明合金表面形成了可以阻碍腐蚀进行的氧化膜。结论 Zn元素可以极大提高TX31合金的耐蚀性。这是由于添加Zn元素后,TXZ311合金腐蚀膜层间的黏附力增加,动态再结晶程度增高,晶粒组织更加均匀,{0001}基面织构强度增加。因此,TXZ311合金的耐蚀性远高于TX31合金。

Residual stress and precipitation of Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu alloy with different quenching rates

The effect of the quenching rate after solution treatment on the residual stress and precipitation behavior of a high strength Mg-5 Zn-3.5 Sn-1 Mn-0.5 Ca-0.5 Cu plate is studied.The simulation results show decreasing temperature gradient in the plate with decreasing quenching rate,which leads to weakened inhomogeneous plastic deformation and decreased residual stress.No dynamic precipitation on the grain boundary happens after either cold water cooling or air cooling,however,air cooling leads to dynamic precipitation of Mg-Zn phase on Mn particles around which a low-density precipitate zone develops after aging treatment.Moreover,the fine and densely distributed Mg-Zn precipitates observed after aging treatment of the cold water cooled alloy are replaced by coarse precipitates with low density for the air cooled alloy.Both the low-density precipitate zone near Mn particles and the coarsening of precipitates are the source of the decrease in hardness and tensile properties of the air cooled alloy.The residual stress drops faster than the hardness with decreasing quenching rate,which makes it possible to lower the residual stress without sacrificing too much age-hardening ability of the alloy.

热挤压Mg-3Sn-1Zn-xCu合金的显微组织与力学性能

研究了添加Cu对热挤压Mg-3Sn-1Zn合金显微组织和力学性能的影响。结果表明:添加少量Cu能显著细化热挤压Mg-3Sn-1Zn合金晶粒,同时在合金中形成具有高热稳定性的CuMgZn相,提高了合金的室温及高温强度和塑性。当Cu含量为0.5%时,热挤压Mg-3Sn-1Zn-0.5Cu合金的晶粒最细,为2.8μm;其强度和塑性最高,室温屈服强度为241 MPa,伸长率为20.3%,150℃时屈服强度为128MPa,室温拉伸力学性能优于挤压态AZ31B合金,高温强度优于铸态AE42合金。

Improved tensile properties of Mg-8Sn-1Zn alloy induced by minor Ti addition

In this study, the influence of minor titanium(Ti) addition on the microstructure and tensile properties of Mg-8Sn-1Zn based alloys were investigated by means of optical microscopy, X-ray diffraction, scanning electron microscopy, energy dispersive spectrometry, and tensile tests. The results showed that Ti can decrease the secondary dendrite arm spacing(SDAS). The tensile strength of the Mg-8Sn-1Zn-Ti alloys is initially increased by increasing the Ti content up to 0.09 wt.%, but subsequently decreased for further increase of Ti content. The improved tensile properties are attributed to the decreased SDAS and refi ned Mg_2Sn phases, as well as the increased fraction of tin(Sn) segregated regions. The tensile fracture surface of the studied alloys shows mixed characteristics of cleavage and quasi-cleavage fracture. Adding Ti does not significantly change the fracture mode of the studied alloys.

高性能Mg-6Sn-3Al-1Zn合金的制备工艺研究

通过改善铸态镁合金制备工艺,得到一种组织均匀、性能优异的Mg-6Sn-3Al-1Zn合金,合金抗拉强度、屈服强度、延伸率分别达到219MPa、82MPa、16%,晶粒尺寸为133.35μm。

Mg-6Sn-3Al-1Zn合金热压缩行为研究

采用Gleeble3500热力模拟机对Mg-6Sn-3Al-1Zn合金在应变速率分别为0.001、0.01、0.1和1 s^(-1),热力模拟机的温度分别为573、623、673和723 K进行了热压缩试验研究。结果表明,Mg-6Sn-3Al-1Zn合金在热变形行为中真应力与压缩温度成反比,但真应力与应变速率成正比。构建了合金的双曲正弦本构模型,揭示了Mg-6Sn-3Al-1Zn合金热加工时的变形机制,以及变形温度、应变速率和流变应力之间的关系。采用峰值应力与应变量分别为0.1、0.3和0.5时的应力,根据动态材料模型理论得到合金的热加工图。结果表明,该合金的最佳加工温度范围和应变速率范围分别为708~723 K和0.001~0.04 s^(-1)。

两道次包套轧制变形量对Mg-6Sn-3Al-1Zn合金组织和力学性能的影响

在450℃下进行不同变形量包套轧制Mg-6Sn-3Al-1Zn合金,包套轧制分两道次,单道次轧制变形量分别为23%、35%和55%,总轧制变形量分别约为40%、60%和80%。结果表明,随着轧制变形量增加,合金中的再结晶晶粒数量增加,平均晶粒尺寸先减小后保持稳定,当变形量分别为40%、60%和80%时,合金的平均晶粒尺寸分别为28.40、6.91和7.01μm。包套轧制后,合金中出现了位错和<c+a>位错。随着轧制变形量增加,<c+a>位错逐渐增多,锥面滑移逐渐占主导作用,并且位错总量增多。当单道次压下率为55%(总轧制量约80%)时,合金由少量的大晶粒和大量细小的动态再结晶晶粒组成,形成明显的双峰组织,此时其屈服强度、抗拉强度和伸长率分别为212MPa、326MPa和20.6%,相对于铸态镁合金分别提升了138.5%、57.5%和62.2%。