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实验装置如图1所示,采用20 kW光纤激光器(λ=1070 nm)可实现0~20 kW的激光输出,激光空间分布呈高斯分布,实验采用光斑直径为2 cm,激光辐照时间为8 s,入射激光功率密度在691~1020 W/cm2之间调节。输出激光束通过平凸透镜L1(f=200 mm),辐照到处于射流气体中的铝合金样品,样品由三维平移台控制。功率计实时记录入射激光功率,通过电脑软件可以调节激光功率大小。用带滤光片的高速摄像机记录激光辐照铝合金前的表面状况。使用巨哥公司生产的红外热像仪记录铝合金前后表面的温度历史,响应时间为6 μm,发射率在0.01~1之间可调,最小的取样间隔为20 nm,温度测量范围为350~3500 ℃。热电偶用耐高温粘合剂附着在铝合金后表面中心点,确定铝合金的真实温升历史,接着用热像仪测量铝合金后表面中心点温度并调节发射率即为铝合金的发射率,热像仪用热电偶定标的发射率为0.07。通过前表面热像仪确定激光出光时刻,后表面热像仪确定铝合金穿孔时刻,利用时间差计算铝合金的穿孔时间。
如图2所示,采用的铝合金样品尺寸为10 cm×10 cm×1 mm,空气压缩机和气流喷嘴提供切向气流,支架将铝合金样品前表面与喷嘴口保持平行并且紧贴前表面,喷嘴口中心同铝合金中心平齐,在激光辐照区域产生较为稳定的切向气流。
根据实验光路、装置介绍实验方案:如表1所示,对1~30号样品按顺序依次进行在0.6 Ma气流速度下激光功率密度(691、751、834、892、951、1020 W/cm2)对铝合金穿孔效应影响的研究;对31~70号样品按顺序依次进行在691 W/cm2激光功率密度下0~0.7 Ma气流速度对铝合金穿孔效应影响的研究。根据红外热像仪记录的铝合金表面温度历史,分析气流速度与激光功率密度对铝合金中心点和穿孔点温度场分布的影响及铝合金表面形貌的变化。每组进行五次重复实验以保证实验结果的准确性。
Type of material Sample number Laser power density/W·cm−2 Air velocity/Ma 7075 aluminum alloy 1-5 691 0.6 6-10 751 11-15 834 16-20 892 21-25 951 26-30 1020 7075 aluminum alloy 31-35 691 0 36-40 0.1 41-45 0.2 46-50 0.3 51-55 0.4 56~60 0.5 61-65 0.6 66-70 0.7 Table 1. Experimental parameters: Laser power density and airflow velocity
Perforation effect of CW laser irradiation on aluminum alloy under subsonic flow
doi: 10.3788/IRLA20210883
- Received Date: 2021-11-23
- Rev Recd Date: 2022-02-13
- Available Online: 2022-03-04
- Publish Date: 2022-02-28
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Key words:
- CW laser /
- subsonic flow /
- temperature field /
- perforation effect
Abstract: The perforation effect of laser irradiated target is different under different airflow velocity. The perforation effect of 7075 aluminum alloy irradiated by 1070 nm CW laser under subsonic airflow(0-0.7 Ma) was experimentally studied. The temperature history, perforation time, perforation aperture and surface morphology of the center point of the aluminum alloy were analyzed. The results show that under the same airflow velocity, with the increase of the incident laser power density, the temperature rise rate of the aluminum alloy surface increases and the equilibrium temperature of the final melting layer increases. The perforation time of aluminum alloy decreases exponentially; the increase rate of pore size decreases exponentially. At the same laser power density, with the increase of airflow velocity, the perforation time of aluminum alloy increases first and then decreases to a stable and then increases. Both the removal rate of melt and the cooling effect of airflow lead to the longest perforation time near 0.1 Ma and the shortest perforation time near 0.3 Ma. The perforation time of 0.6 Ma is roughly equal to that of 0 Ma about 5.5 s. With the increase of airflow velocity, the cooling effect increases, and there is no perforation in the aluminum alloy after 0.7 Ma. Convection cooling leads to rapid condensation of the melt, and the removed melt concentrates in the downstream area of the airflow.