高功率密度激光重熔镁合金的非均匀性机理研究

Study on Inhomogeneity Mechanism of High Power Density Laser Remelting Magnesium Alloy

采用额定功率为3 kW的Nd:YAG固体激光器,开展镁合金激光重熔试验,通过金相显微镜(TK-C1031EC)、扫描电镜、X射线衍射(XRD)和维氏显微硬度计表征试样的组织、物相和硬度。结果表明:由于激光重熔镁合金存在匙孔现象,试样横截面形貌为短螺栓形;在高能量密度激光重熔下,熔凝过程中的预热作用、熔凝层的热传导等综合影响,使能量累积达到了镁合金熔凝的临界能量,沿激光扫描方向,镁合金的熔深逐渐增加;激光熔凝区域的晶粒细化;在热影响区温度介于α-Mg相及β相时,该区域观察到局部熔化现象,且热影响区Mn-Al相变细小;沿激光扫描方向展现出很好的预热作用,熔池内温度呈增加的趋势,沿扫描方向硬度呈逐渐下降的趋势。

The laser remelting experiment was carried out for a magnesium alloy by using a Nd:YAG solid-state laser with a rated power of 3 kW.The microstructure,phase and hardness of the sample were characterized by metallographic microscope(TK-C1031EC),scanning electron microscopy(SEM),X-ray diffraction(XRD)and Vickers microhardness tester(HVS-1000Z).The results show that,the cross section of the sample is short bolt shape due to the phenomenon of key hole in laser remelting magnesium alloy.Under the condition of high energy density laser remelting,the preheating effect in the melting process and the heat conduction of the melting layer make the energy accumulation reach the critical energy of magnesium alloy melting.The melting depth of the magnesium alloy is gradually increased along the laser scanning direction.The grain is refined in laser fused zone.When the temperature in the heat-affected zone is between theα-Mg phase and theβphase,local melting is observed in the region,and the Mn-Al phase in the heat-affected zone is refined.It shows a good preheating effect along the laser scanning direction,the temperature in the molten pool increases,and the hardness decreases gradually along the scanning direction.