远离平衡态下镁合金表面激光重熔强化的研究

Laser Surface Melting and Strengthening Magnesium Alloy Far from Equilibrium

摘要:

为了在镁合金表面获得远离平衡态的极端快速冷却结构，对AZ31B镁合金进行了在液氮环境下极端快速冷却的CO2激光表面重熔处理，并对该重熔层的微观结构、性能和强化机制进行了分析研究。研究结果表明：远离平衡态结晶凝固的镁合金表面重熔层的晶粒高度细化，且晶粒大小基本均一。重熔层主要为α-Mg，以及沿晶界析出的极少量β-Mg17Al12。极端快速冷却条件获得的远离平衡态的重熔层的强化机制主要为细晶强化、超固溶强化和位错强化。在此强化作用下重熔层的显微硬度提高到140HV，磨损失量比空气冷却条件下的少50%，耐磨性显著提高。该重熔层的冲击断口特征显示出了塑性变形的痕迹，故该镁合金表面的塑性和韧性也得到了改善。

Abstract:

In order to obtain extremely rapid solidification structure far from equilibrium, the surface of AZ31B magnesium alloy was melted by CO2 laser, while the samples were extremely rapidly cooled in liquid nitrogen. Microstructure, performance and strengthening mechanism of laser melted layer were investigated. The results showed that grains of melted layer were highly refined and grain size was nearly uniform. The melted layer contained α-Mg and β-Mg17Al12, but β-Mg17Al12 which distributed along grain boundary was few. Because of strengthening mechanisms of fined grains, super solid solution and dislocation, microhardness of melted layer was up to 140HV. Wear loss of melted sample cooled in liquid nitrogen was about 50% less than that of the untreated sample and melted sample cooled in air, and wear resistance of melted layer was improved obviously. Impacting fracture morphology indicated that there was trace of plastic deformation, thus, plasticity and ductility were also improved.