AZ91D压铸镁合金激光局部重熔区气孔的形成机制

采用扫描电镜(SEM)、X光电子能谱分析仪(XPS)等分析手段,研究了NiTi合金表面绝缘膜的结构及成分,从而探讨非阀金属NiTi合金表面微弧氧化陶瓷膜层的形成机制.结果表明,NiTi合金微弧氧化过程中的电流密度-时间曲线与纯钛形状基本一致,也可分为3个阶段,但其最大的电流密度为后者的13倍;NiTi合金表面的绝缘膜主要是通过电化学沉积形成的Al2O3及少量的TiO2、Ni2O3和磷酸盐薄膜,这一绝缘膜就相当于阀金属的阳极氧化膜,为NiTi合金进行微弧氧化处理提供了前提条件;NiTi合金表面的陶瓷膜层主要来源于电解液中的铝酸根离子和少量的基体Ni和Ti(包括固态的和溶解于电解液中离子态的),经反复的放电、熔融、喷射、冷却、凝固,发生一系列的电化学、等离子体化学和热化学反应最终形成表面粗糙多孔陶瓷膜层.

Pore Formation Mechanism in Laser Local Re-melted Areas of Die Cast Magnesium Alloy AZ91D

The structure and composition of the dielectric film on NiTi alloy surface were investigated by scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS) to discuss the formation mechanism of the micro-arc oxidation (MAO) ceramic coatings on non-valve metal NiTi alloy surface. The results show that during the MAO process the shape of the current density-time curve of the NiTi alloy is nearly consistent with that of titanium and can also be divided into three stages; however, the maximum current density is 13 times higher than that of the latter. The dielectric film on NiTi alloy surface is formed through electrochemical deposition, and mainly composed of Al2O3 and a little TiO2, Ni2O3 and phosphate. This dielectric film can be acted as the anodic oxide film of the valve metals to provide the precondition of the MAO treatment. The ceramic coating on NiTi alloy is mainly from the aluminum ion in electrolyte and a small amount of substrate Ni and Ti (including solid state and ion state dissolved in the electrolyte), and through repeated discharge, melting, injection, cooling and solidification, and a series of electrochemical, plasma chemical and thermal chemical reactions, at last forms the rough and porous ceramic coating on the surface of NiTi alloy