激光清洗中振镜扫描速度对7075铝合金表面质量和摩擦特性的影响

doi:10.12382/bgxb.2022.0437

摘要/Abstract

摘要：

采用脉冲激光对7075铝合金表面原始氧化膜进行了激光清洗实验,探究振镜扫描速度对7075铝合金清洗表面形貌、氧含量和物相组成的影响规律,通过激光共聚焦显微镜和摩擦磨损试验机研究了7075铝合金的表面粗糙度和耐磨性能。研究结果表明:随着振镜扫描速度从2500mm/s 增加至4500mm/s,清洗表面氧含量和粗糙度均呈现先减小、后增大的趋势,当扫描速度为3500mm/s时,表面氧含量和粗糙度均达到最低,分别为1.45%和0.344μm,当扫描速度为2500mm/s时,清洗表面会出现严重的熔融现象,光斑凹坑以及波纹状凸起使得清洗表面粗糙度增大,当扫描速度小于等于3000mm/s时,清洗表面会发生热氧化,生成了主要由Al₂O₃组成的新的氧化膜;激光清洗后,粗糙度较小的熔融层可提高清洗表面减摩耐磨性;在10N的摩擦载荷下,严重熔融的清洗表面在摩擦过程中会发生疲劳剥落;清洗表面磨损机制主要以磨粒磨损和剥层磨损为主。

关键词: 激光清洗, 表面形貌, 粗糙度, 摩擦特性

Abstract:

The laser cleaning experiment of the original oxide film on the surface of 7075 aluminum alloy was carried out by pulsed laser. The effects of galvanometer scanning speed on the surface morphology, oxygen content and phase composition of 7075 aluminum alloy were investigated. The surface roughness and wear resistance of 7075 aluminum alloy were studied by laser confocal microscope and friction and wear tester. The results show that, as the scanning speed of galvanometer increases from 2500mm/s to 4500mm/s, the oxygen content and roughness of the cleaned surface first decrease and then increase. When the scanning speed is 3500mm/s, the surface oxygen content and roughness reach the lowest, which are 1.45% and 0.344μm, respectively. When the scanning speed is 2500mm/s, a serious melting phenomenon appears on the cleaned surface, and the spot pits and corrugated bulges make the cleaned surface roughness increase. When the scanning speed is less than or equal to 3000mm/s, a thermal oxidation occurs on the cleaned surface, and a new oxide film mainly composed of Al₂O₃ is formed. After laser cleaning, the molten layer with small roughness can improve the antifriction and wear resistance of the cleaned surface. Under the friction load of 10N, a fatigue spalling occurs on the heavily molten cleaned surface during the friction process. The wear mechanism of cleaning surface is mainly abrasive and delamination wears.

Key words: laser cleaning, surface topography, roughness, friction characteristics

中图分类号:

TN249

王蔚, 沈杰, 刘伟军, 邢飞, 张凯, 李强, 于兴福. 激光清洗中振镜扫描速度对7075铝合金表面质量和摩擦特性的影响[J]. 兵工学报, 2023, 44(10): 2995-3005.

WANG Wei, SHEN Jie, LIU Weijun, XING Fei, ZHANG Kai, LI Qiang, YU Xingfu. Effect of Galvanometer Scanning Speed on Surface Quality and Friction Characteristics of 7075 Aluminum Alloy During Laser Cleaning[J]. Acta Armamentarii, 2023, 44(10): 2995-3005.

图/表 20

图1 激光清洗原理示意图

Fig.1 Schematic diagram of laser cleaning principle

表1 激光清洗主要工艺参数

Table 1 Main process parameters of laser cleaning

工艺参数	数值
波长/nm	1064
扫描速度/(mm·s^-1)	2500, 3000, 3500, 4000, 4500
激光平均功率/W	110
激光光斑直径/mm	0.7
重复频率/kHz	20
脉宽/ns	60

图2 原始表面元素成分

Fig.2 Composition of original surface elements

图3 不同扫描速度清洗后的试样形貌

Fig.3 Sample morphologies after cleaning at different scanning speeds

图4 激光清洗前后试样微观形貌

Fig.4 Microstructures of sample before and after laser cleaning

图5 清洗表面烧蚀现象

Fig.5 Ablation of cleaned surface

图6 不同扫描速度下光斑搭接处的温度变化示意图

Fig.6 Schematic diagram of temperature change at spot overlap under different scanning speeds

图7 清洗表面化学成分

Fig.7 Chemical composition of cleaned surface

表2 7075铝合金及其表面3种氧化物的熔点

Table 2 Melting points of 7075 aluminum alloy and three oxides on its surface

材料	7075铝合金	Al₂O₃	MgO	MgAl₂O₄
熔点/℃	475~635	2054	2852	2130

图8 热氧化示意图

Fig.8 Schematic diagram of thermal oxidation

图9 液态氧化膜熔池流程图

Fig.9 Flow diagram of molten pool of liquid oxide film

图10 扫描速度对清洗表面粗糙度的影响

Fig.10 Effect of scanning speed on cleaned surface roughness

图11 不同扫描速度下7075铝合金表面原始氧化膜粗糙度变化示意图

Fig.11 Schematic diagram of roughness change of original oxide film on 7075 aluminum alloy surface at different scanning speeds

图12 7075铝合金原始表面在不同载荷下的干摩擦磨损形貌

Fig.12 Dry friction and wear morphology of 7075 aluminum alloy under different loads

图13 7075铝合金原始表面在不同载荷下的摩擦系数

Fig.13 Friction coefficients of 7075 aluminum alloy under different loads

图14 干摩擦条件下不同扫描速度清洗后的磨损形貌(载荷1N)

Fig.14 Wear morphology after cleaning at different scanning speeds under dry friction conditions (Load 1N)

图15 干摩擦条件下不同扫描速度清洗后的磨损形貌(载荷5N)

Fig.15 Wear morphology after cleaning at different scanning speeds under dry friction conditions (Load 5N)

图16 干摩擦条件下不同扫描速度清洗后的磨损形貌(载荷10N)

Fig.16 Wear morphology after cleaning at different scanning speeds under dry friction conditions (Load 10N)

表3 不同振镜扫描速度清洗前后7075铝合金的磨损量

Table 3 Wear amounts of 7075 aluminum alloy before and after cleaning at different galvanometer scanning speeds mg

振镜扫描速度/ (mm·s^-1)	摩擦载荷/N
振镜扫描速度/ (mm·s^-1)	1	5	10
原始表面	0.6	3.4	8.3
2500	0.4	3.1	8.8
3000	0.2	2.5	7.5
3500	0.2	2.5	7.6
4000	0.3	2.7	7.7
4500	0.6	3.1	8.1

图17 干摩擦条件下不同扫描速度清洗后的表面摩擦系数变化

Fig.17 Variation curves of surface friction coefficient after cleaning at different scanning speeds under dry friction condition

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