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-  2018 


DOI: 10.11951/j.issn.1005-0299.20170019

Keywords: 等通道转角挤压,超细晶纯铝,微观组织,力学性能,耐腐蚀性能

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在室温下采用等通道转角挤压(ECAP)对工业纯铝(CP-Al)圆棒料进行12道次挤压,通过光学显微镜(OM)、X射线衍射(XRD)、扫描电子显微镜(SEM)、单向拉伸与电化学测试研究了超细晶纯铝的微观组织、力学性能和耐腐蚀性能.结果表明,ECAP后纯铝试样晶粒细化,4道次和8道次后晶粒尺寸分别达到576、482 nm.同时,显微硬度和抗拉强度显著提高,由初始的26.8 HV、79.2 MPa分别增加到8道次的48.3 HV、146.4 MPa,而塑性有所降低,断裂伸长率由初始的22.1%降低到4道次的9.5%.在质量分数为3.5% NaCl溶液中进行了开路电位(OCP)、极化曲线(PD)及电化学阻抗谱(EIS)测试,并观察腐蚀形貌.研究表明,随着ECAP道次的增加,腐蚀电位正移(-0.965 ~-0.860 V)、电荷传递电阻增大(1.741×104~4.798 × 104 Ω·cm2)、点蚀电位正移(-0.818~-0.734 V)、腐蚀电流密度降低(12.910~3.288 μA/cm2),且腐蚀形貌有所改善,表明其耐腐蚀性能提高.这是由于随着挤压道次的增加,晶粒细化,加速了表面钝化膜的形成,形成的钝化膜更为致密,从而降低了腐蚀速率.
Commercial pure aluminum (CP-Al) was pressed up to 12 passes at room temperature (RT) by equal channel angular pressing (ECAP). The microstructure, mechanical properties and corrosion resistant properties of the ultra-fine grained commercial pure aluminum (CP-Al) were fully investigated by optical microscope (OM), X-ray diffraction (XRD), uniaxial tensile tests, scanning electron microscope (SEM) and electrochemical tests. The experimental results suggested that the grains were refined as the number of ECAP passes increased, the grain size was 576 nm and 482 nm after 4 and 8 passes, respectively. The micro-hardness and tensile strength increased obviously from 26.8 HV, 79.2 MPa to 48.3 HV, 146.4 MPa after 4 passes and 8 passes while the elongation educed from 22.1% to 9.5% after 4 passes. The OCP, PD, EIS electrochemical test with 3.5%(mass fraction) NaCl solution was performed, and the corrosion morphology was observed. Experiment results also showed that the ultra-fine grained CP-Al had higher positive corrosion potential (-0.965 V to -0.860 V), higher charge transfer resistance (1.741×104 Ω·cm2 to 4.798 ×104 Ω·cm2), higher positive pitting potential (-0.818 V to -0.734 V) and lower corrosion current density (12.910 A/cm2 to 3.288 A/cm2) while the corrosion morphology also showed that the ultra-fine grained CP-Al had higher corrosion resistance. This is because small grain size accelerates the formation of passivation film on the sample surface, resulting in decrease in the corrosion rate.


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