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摘要: 采用自制的板帶高溫摩擦試驗機模擬實際固溶–沖壓–淬火一體化熱成形工藝下7075鋁合金的高溫摩擦過程，分別對上下摩擦頭進行冷卻和加熱以模擬實際熱沖壓過程對模具和壓邊圈的冷卻和加熱，分析了下模加熱溫度、法向載荷和滑動速度對7075鋁合金摩擦行為及磨損機理的影響。結果表明：鋁合金摩擦系數隨著下模加熱溫度的升高而增大，磨損機制由300 ℃時的黏著磨損轉變為500 ℃時的黏著磨損、氧化磨損和磨粒磨損；施加法向載荷越大，摩擦系數越大，不同載荷下磨損機制均為黏著磨損及輕微的磨粒磨損，且隨著載荷增大，黏著磨損程度有所加深；高滑動速度導致了磨損表面局部氧化物的生成，使摩擦系數隨著滑動速度增大而減小，滑動速度為30 mm·s?1時，磨損機制主要是氧化磨損、磨粒磨損和黏著磨損。Abstract: Aluminum alloys are lightweight materials widely used in the automobile industry because of their high specific strength. As the aluminum alloy with the highest strength at room temperature, 7075 aluminum alloy has great potential for usage in the manufacturing of structural parts. However, its formability at room temperature is poor and its springback is large. Although both good formability and high strength in aluminum alloys can be realized by hot forming, 7075 aluminum alloy has high susceptibility to adhesive wear, which means its tribological properties are poor during hot forming. Exploration of the influence of process parameters on the friction behavior and wear mechanism of 7075 aluminum alloy has great significance for the numerical simulation of the hot-stamping process and lubrication engineering. The high-temperature friction process of 7075 aluminum alloy during the actual hot forming–quenching integrated process was simulated by a self-made high-temperature strip friction tester. The upper and lower friction components were cooled and heated, respectively, to simulate the cooling and heating of the die (blank holder) in the actual hot-stamping process. The effects of the preheating temperature of the lower die, normal load, and sliding speed on the friction behavior and wear mechanism of 7075 aluminum alloy were analyzed. The results show that the friction coefficient of aluminum alloy increases with increase in the preheating temperature, and the wear mechanism changes from adhesive wear at 300 °C to adhesive, abrasive, and oxidative wear at 500 °C. The larger the normal load applied, the larger is the friction coefficient. The wear mechanism under different loads was determined to be adhesive wear with slight abrasive wear, with the degree of adhesive wear increasing with the increase in load. A high sliding speed leads to the formation of local oxides on the surface, which makes the friction coefficient decrease with an increase in the sliding speed. The main wear mechanisms are oxidative, abrasive, and adhesive wear when the sliding speed is 30 mm·s?1.
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Key words:
- hot stamping /
- 7075 aluminum alloy /
- high-temperature friction /
- friction coefficient /
- wear mechanism
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圖 1 板帶高溫摩擦試驗機（a）及加載系統細節（b）
Figure 1. Photographs of the high-temperature strip friction tester (a) and details of the loading system (b)
1—stepping motor; 2—ball screw; 3—force sensor; 4—lever; 5—furnace; 6—controller; 7—recorder; 8—temperature control box
圖 3 不同下模加熱溫度下7075鋁合金的摩擦系數
Figure 3. Friction coefficient of 7075 aluminum alloy at different temperatures of lower die
圖 4 不同下模加熱溫度下7075鋁合金的磨損表面形貌。（a）300 ℃；（b）400 ℃；（c）500 ℃
Figure 4. SEM micrographs of the worn surfaces of 7075 aluminum alloy at different temperatures of lower die: (a) 300 ℃；(b) 400 ℃；(c) 500 ℃
圖 5 不同法向載荷下7075鋁合金的摩擦系數
Figure 5. Friction coefficient of 7075 under different normal loads
圖 6 不同法向載荷下7075鋁合金的磨損表面形貌。（a）540 N；（b）680 N；（c）820??? N
Figure 6. SEM micrographs of the worn surfaces of 7075 aluminum alloy under different normal loads: (a) 540 N；(b) 680 N；(c) 820??? N
圖 7 不同滑動速度下7075鋁合金的摩擦系數
Figure 7. Friction coefficients of 7075 aluminum alloy at different sliding speeds
圖 8 不同滑動速度下7075鋁合金的磨損表面形貌及EDS分析。（a）滑動速度為10 mm·s?1時的試樣磨損形貌；（b）滑動速度為20 mm·s?1時的試樣磨損形貌；（c）滑動速度為20 mm·s?1時的EDS分析；（d）滑動速度為30 mm·s?1時的試樣磨損形貌；（e）滑動速度為30 mm·s?1時的EDS分析
Figure 8. SEM micrographs of the worn surfaces and EDS analyses of 7075 aluminum alloy at different sliding speeds: (a) wear morphology of specimen when sliding speed is 10 mm·s?1; (b) wear morphology of specimen when sliding speed is 20 mm·s?1; (c) EDS analysis when sliding speed is 20 mm·s?1; (d) wear morphology of specimen when sliding speed is 30 mm·s?1; (e) EDS analysis when sliding speed is 30 mm·s?1
表 1 7075鋁合金的化學成分（質量分數）
Table 1. Chemical composition of 7075 aluminum alloy
% Element Zn Mg Cu Cr Fe Mass fraction 6.10 2.54 1.20 0.20 0.20 
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表 2 H13鋼的化學成分（質量分數）
Table 2. Chemical composition of H13 steel
% Element C Si Mn Cr P S Mo B V Mass fraction 0.391 0.911 0.374 5.180 0.015 0.015 1.450 0.003 0.953
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表 3 高溫摩擦試驗參數
Table 3. Experimental parameters of the high-temperature friction test
Test group Temperature of lower
die /℃Normal load /
NSliding speed /
(mm·s?1)1 300, 400, 500 540 10 2 400 540, 680, 820 10 3 400 540 10, 20, 30
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Test point O Mg Al Fe Cu 1 21.27 3.50 24.49 4.88 45.86 2 22.60 4.90 33.40 5.28 33.83
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表 5 不同載荷下試樣磨損表面元素的EDS分析（質量分數）
Table 5. EDS analysis of worn surface elements under different normal loads
% Test point Mg Al Fe Cu Zn A 1.42 93.56 0.93 1.60 2.49 B 4.69 88.67 1.52 1.51 3.61 C 2.47 88.40 2.58 1.60 4.95
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