Effect of Galvanometer Scanning Speed on Surface Quality and Friction Characteristics of 7075 Aluminum Alloy During Laser Cleaning

doi:10.12382/bgxb.2022.0437

Abstract

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

CLC Number:

TN249

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.

Figures/Tables 20

Fig.1 Schematic diagram of laser cleaning principle

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

Fig.2 Composition of original surface elements

Fig.3 Sample morphologies after cleaning at different scanning speeds

Fig.4 Microstructures of sample before and after laser cleaning

Fig.5 Ablation of cleaned surface

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

Fig.7 Chemical composition of cleaned surface

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

Fig.8 Schematic diagram of thermal oxidation

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

Fig.10 Effect of scanning speed on cleaned surface roughness

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

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

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

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

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

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

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

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

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