T6处理对AZ63镁合金在模拟海水中耐蚀性的影响

为研究热处理工艺对合金耐腐蚀性的影响,采用X射线衍射仪(XRD)、扫描电镜(SEM)、析氢失重以及多种电化学测试等方法研究了经T6处理(固溶处理+人工时效)的AZ63镁合金在模拟海水中的腐蚀行为。结果表明:T6处理(固溶处理+人工时效)镁合金第二相沿晶界呈网状分布,与铸态镁合金相比氢气析出多、腐蚀速度快,并有点蚀产生;T6处理(固溶处理+人工时效)改变了镁合金的组织结构以及分布,增大了稳定相第二相与基体相的接触,降低了合金的耐蚀性。     

AZ31镁合金在Hank’s模拟体液中的腐蚀行为研究

研究了AZ31镁合金在Hank's模拟体液中的腐蚀行为,包括腐蚀形貌、腐蚀速度和腐蚀电化学特征参数.通过扫描电子显微镜(SEM)比较了不同腐蚀环境中镁合金样品的腐蚀形貌特征.利用失重法测量了镁合金的腐蚀速度,并依此分析了Hank's模拟体液中各成分对镁合金腐蚀速度的影响.测量并分析了不同pH值下的动电位动态极化曲线.结果表明,镁合金在Hank's模拟体液中的腐蚀主要为氯离子引起的点蚀;H_2PO_4~-和HPO_4~(2-)具有缓蚀作用;pH值的升高可以提高镁合金腐蚀反应的自腐蚀电位,降低腐蚀反应的热力学倾向,稳定腐蚀过程中形成的钝化膜,从而降低了腐蚀速度.     

AZ31镁合金在含NaCl和Na2SO4薄层液膜下的腐蚀行为

为研究大气污染物对镁合金腐蚀的影响规律,采用室内模拟暴露实验,分析AZ31镁合金含有NaCl和Na2SO4的薄层液膜下的电化学腐蚀行为.结果表明:AZ31镁合金表面沉积NaCl和Na2SO4薄液层中的腐蚀动力学符合幂函数规律,说明NaCl和Na2SO4对AZ31镁合金腐蚀有加速作用;AZ31镁合金在NaCl薄层液膜下,阳极极化电流密度增大,R f和R ct值降低,促进了阴极去极化历程,增强了阳极活性溶解,加剧镁合金的阳极溶解;而在Na2SO4薄层液膜下,R f和R ct值增大,击穿电位与腐蚀电位的差值(ΔE)减小,这是由于难溶的硫酸盐和Mg(OH)2覆盖在AZ31镁合金表面,使金属溶解和离子扩散速率降低,导致阳极过程阻滞.     

模拟体液中的尿酸对AZ31B镁合金腐蚀行为的影响

过去,探讨高尿酸浓度体液中AZ31B镁合金腐蚀状况的研究不多。采用开路电位、交流阻抗谱和失重法等研究了AZ31B镁合金在不同尿酸浓度的模拟体液中的腐蚀行为。结果表明:在模拟体液中尿酸会加快镁合金的腐蚀,但是尿酸加入量与腐蚀速度不是简单的线性关系,尿酸浓度较小时其对腐蚀速率影响较大,当尿酸浓度超过104μmol/L后,镁合金的腐蚀速率不再显著增大;镁合金的失重速率随着浸泡时间的延长而减小,经8~12 d的浸泡后,镁合金的腐蚀过程基本达到稳定状态。     

累积叠轧焊温度对AZ31镁合金板材组织与性能的影响

目的研究叠轧温度对AZ31镁合金板材组织与性能的影响。方法在450℃和550℃下,对AZ31镁合金板材进行2道次叠轧,研究不同温度下板材界面裂纹的金相组织、RD-ND面晶体取向、力学性能以及断面形貌的异同。结果 450℃累积叠轧制备的ARB2镁合金板材室温断裂伸长率为2.3%,550℃累积叠轧制备的ARB2镁合金板材室温断裂伸长率为8%;450℃叠轧板材中动态再结晶晶粒大多数尺寸约为1～3μm左右,550℃叠轧板材中动态再结晶晶粒大多数尺寸约为600 nm～2μm。结论通过提高温度,可改善界面结合性能,促进基面晶粒往非基面取向偏转,提升了叠轧板材的力学性能,使叠轧板材由较低温度下的脆性断裂向韧性断裂转变。     

混合稀土对AZ91镁合金在NaCl溶解中的腐蚀行为影响

通过静态失重法，极化曲线和交流阻抗测试研究了混合稀土（Re)对AZ91镁合金腐蚀行为的影响。结果表明：Re的加入使AZ91微观组织得到改善，减缓了AZ91镁合金在NaCl溶液中的腐蚀。     

苯甲酸钠对AZ31镁合金的缓蚀作用

发展适用于镁合金的环保型缓蚀剂对于有效抑制镁合金腐蚀、拓展其应用具有重要意义.苯甲酸钠(SB)作为缓蚀剂对镁合金的作用过去报道较少.为此,采用电化学阻抗谱(EIS)、极化曲线、扫描电子显微镜(SEM)等方法研究了苯甲酸钠对AZ31镁合金在3.5%NaCl腐蚀介质中的缓蚀作用.结果表明:SB是一种阳极型缓蚀剂,通过增大阳极极化有效抑制了AZ31镁合金的腐蚀;缓蚀率随SB浓度的增大而增加,可达87%以上;SB的缓蚀作用主要由在金属表面的吸附引起,在AZ31镁合金表面的吸附符合Temkin吸附模型.     

AZ31镁合金管材挤压成型数值模拟与实验研究

运用基于AZ31镁合金本构方程与ALE算法的HyperXtrude软件对典型AZ31薄壁管材的挤压过程进行数值模拟,并通过调整焊合室高度、焊合室大圆角及焊合室坡度3个结构参数,分析不同条件下应力分布与速率分布的变化情况。结果表明:焊合室内近工作带处压力随焊合室高度增加不断减小,分流孔与焊合室压力的最大值与平均值均随焊合室大圆角增大发生降低,分流孔与焊合室压力随焊合室入口坡度增大不断增大,并在焊合室高度为16mm、大圆角为18mm以及入口坡度为15°时金属流速均方差达到最小值。优化模具结构缓解了应力集中与流速不均等问题,在实验生产中得到合格产品,型材组织均匀细化。     

循环道次对高温叠轧AZ31镁合金板材组织与性能的影响

目的通过高温累积叠轧工艺制备出高强度的镁合金,并研究该过程中循环道次对AZ31镁合金板材的微观组织与性能的具体影响。方法对累积叠轧1～5次板材进行微观组织观察,并进行显微硬度的测试,得到不同板材的硬度值,通过X射线衍射分析得到不同板材的取向结果,最终进行力学性能实验,并对比分析。结果随着循环道次的增加,板材抗拉强度有明显改变。从260 MPa先增加至310 MPa,最后稳定在350 MPa左右;非基面织构比重增加;断裂伸长率先降低后升高并稳定在10%左右。结论累积叠轧工艺使得AZ31镁合金板材产生了加工硬化,并显著细化了晶粒。循环道次的增加、孪晶产生和晶界数量显著增多导致强度进一步提高。     

AZ31镁合金轧制工艺的研究

对AZ31镁合金在400℃条件下的轧制工艺进行了研究,在不同压下量、不同道次条件下分别进行了轧制实验,并对轧制后AZ31板材的组织和力学性能进行了研究。实验结果表明:在400℃条件下,以小变形量轧制,每道次压下量为1mm时,较好的加工工艺条件为轧制到第8道次,累积变形量50%;每道次轧制压下量为2mm时,较好的加工工艺条件为轧制到第2道次,累积变形量为25%;AZ31镁合金在大变形量下轧制易产生裂纹,裂纹的产生可能是由于随着累积变形量增加,内应力激增,在难变形的硬取向晶粒区或第二相处产生应力集中,萌生裂纹。裂纹尖端扩展经过的区域变形量较大,因而裂纹两侧存在再结晶细晶区域。     

AZ31镁合金非等温拉深性能的研究

针对AZ31镁合金等温拉深性能差的问题,提出了AZ31镁合金的非等温拉深工艺.通过平底杯形冲头拉深试验研究了不同冲头温度和板料温度对AZ31镁合金非等温拉深性能的影响,确定了使AZ31镁合金具有最佳拉深性能的板料和冲头温度范围.实验结果表明,除了板料和冲头温度之外,拉深速度和润滑条件对AZ31镁合金的非等温拉深性能也有重要影响.     

AZ31B镁合金带材热轧过程组织均匀性及性能研究

本文开展了变形温度为300、350、400 ℃和总压下率分别为15%、30%、45%、60%的AZ31B镁合金带材热轧试验,分析了不同工艺参数对轧后带材的微观组织及力学性能的影响规律。研究表明:随着轧制温度的升高,再结晶百分数增加,晶粒细化显著,组织均匀性增强;当温度达到350 ℃时,由于中间退火保温导致再结晶晶粒长大,使温度进一步升高,对再结晶程度的影响减弱,轧后带材晶粒度和延伸率均有降低;相比温度参数,提升总压下率对晶粒细化效果更为显著,轧制温度为300 ℃,压下率为60%时近表面平均晶粒尺寸由10 μm细化至3.7 μm,中心层晶粒尺寸细化至4.9 μm,组织分布较为均匀;压下率的增加有效改善了组织均匀性,使轧后带材延伸率显著增加,拉伸断口的韧窝增多,且逐渐加深。     

Effect of D-fructose on the in-vitro corrosion behavior of AZ31 magnesium alloy in simulated body fluid

The effect of addingd-fructose to simulated body fluid(SBF) on the corrosion behavior of AZ31 magnesium(Mg) alloy at 37.C and at a pH of 7.4 was studied by potentiodynamic polarization(PDP), electrochemical impedance spectroscopy(EIS), potentiostatic polarization and hydrogen(H2) collecting techniques,Raman spectroscopy technique, scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), X-ray diffraction(XRD), X-ray photoelectron spectroscopy analysis(XPS) and Fourier transformed infrared(FTIR). The results demonstrated that the addition of fructose enhanced the deposition of phosphates forming thick and compact corrosion products, which inhibited the transmission of aggressive ions into the Mg substrate. As a result, both the anodic dissolution of Mg and negative difference effect(NDE) were suppressed. Thus, the corrosion resistance of AZ31 Mgalloy in SBF was significantly improved.     

Corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions

The corrosion behavior of AZ91 magnesium alloy in dilute NaCl solutions was studied using electrochemical measurements, whereby a corrosion map in terms of electrode potential and chloride concentration [Cl⁻] was obtained. AZ91 alloy exhibited the corrosion and passivation zones in dilute NaCl solutions. The passivation zone became narrow with increasing [Cl⁻]. The values of open-circuit potential were in the passivation zone when the [Cl⁻] was less than 0.5 mol/L. XRD patterns showed the presence of the Mg(OH)₂, Mg₅(CO₃)₄(OH)₂·8H₂O and MgO phases in the corrosion product, whereas the latter two phases found in the passive film.     

AZ31镁合金室温异步轧制的织构演变

采用异步轧制技术研究了轧制工艺对AZ31镁合金塑性变形和微取向流变行为的影响.结果表明:将AZ31镁合金板材在室温条件下进行单道次异步轧制,织构随着速比增加,与快、慢辊侧相接触的表面层明显不同,但中间区域变化不明显.在快速辊侧,主要织构组份随着速比的增加而迅速增加;在慢速辊侧,主要织构组份随着速比的增加而交替变化.形变量的增大,可以细化晶粒和改善力学性能.     

AZ31镁合金环境友好阳极氧化处理研究

通过正交试验得到AZ31镁合金无铬、无强氧化物的阳极氧化处理配方及工艺,运用扫描电子显微镜、X射线衍射分析及电化学测试系统对阳极氧化膜的组织结构与耐蚀性进行了表征。结果表明,该环境友好阳极氧化工艺可在AZ31镁合金表面形成具有一定耐蚀性的阳极氧化膜;所得阳极氧化膜表面质量好,是一种多孔的陶瓷膜,膜的物相主要是晶态的MgO、ZnO、Mg以及非晶态的MgAl2O4、Mg18Al23等;阳极氧化处理试样的自腐蚀电流密度减小,而腐蚀电位有所提高,说明镁合金表面形成的阳极氧化膜提高了镁合金表面的耐腐蚀性能。     

热挤压工艺对AZ31镁合金晶粒大小及性能的影响

对商用AZ31镁合金挤压棒材进行了不同工艺参数的挤压变形,系统研究了挤压工艺参数对AZ31镁合金晶粒大小以及性能的影响,并对镁合金组织的微晶尺寸进行了金相定量分析.研究结果表明,热变形可有效细化晶粒,但对AZ31镁合金晶粒细化是有限度的;对已通过热挤压变形晶粒细化的AZ31镁合金进一步进行大的塑性变形,其晶粒不但没有进一步的细化反而比挤压前略有长大.     

Temperature evolution analysis of AZ31B magnesium alloy during quasi-static fracture

Fracture toughness of AZ31B magnesium alloy subjected to quasi-static loading was investigated by infrared thermography. The results showed that temperature evolution around the crack propagation path during fracture underwent three stages: initial steady stage, monotonic increase stage and final steady stage. The temperature increase at the beginning of stage II is nearly corresponding to the initiation of unstable crack propagation. And based on this phenomenon, a method applying infrared thermography to estimate fracture toughness of AZ31B magnesium alloy was proposed. Fracture toughness was calculated through infrared thermography, which was in good agreement with the result determined by traditional standard method. Finally, the fracture mechanism was investigated.     

Rotation friction pressing riveting of AZ31 magnesium alloy sheet

A kind of joining method for magnesium alloys, rotation friction pressing riveting (RFPR), is proposed in this paper. In RFPR operation, a rivet with a plug rotating at high speed is brought to contact with the riveted sheets, generating frictional heat between the rivet and riveted sheets, which softens the sheet materials and enables the rivet to be drilled into the sheets under reduced force. When fully inserted, the rivet is stopped rotating, and the plug is immediately pressed into the shank of the rivet by a punch. The expansive deformation of the rivet shank occurs under the action of the plug, thereby forming a mechanical interlock between the rivet and the sheets to fasten the sheets together. The studies show that RFPR of AZ31 magnesium alloy sheet can be carried out at ambient temperature, and provides the joints with superior shear strength and fatigue property when compared with self-piercing riveting (SPR). The effects of the operating parameters of RFPR process on the quality of the joints were investigated in the study. The results shows that while the rivet rotation speed little affects the shear strength of RFPR joints, the punch pressure has a significant influence on the mechanical properties of the RFPR joints. A numerical analysis was also performed to understand the effect of the punch pressure on the interlock between the rivet and the sheets, and the stress and strain distribution inside the sheet materials around the rivet. The results show that the interlock increased with the punch pressure and there is residual compressive stress inside the sheet materials, which seems to explain the good fatigue property of RFPR joints observed.