We report herein on the preparation of a superhydrophobic surface by high-speed wire electrical discharge machining on the surface of a 7075 aluminium alloy without any chemical treatment. The morphology and the anti-icing, anti-wear and anti-corrosion properties of the superhydrophobic surface were characterised by scanning electron microscopy, contact angle measurements, a custom-made experimental apparatus, a universal mechanical tester and an electrochemical workstation, respectively. Our results indicated that the superhydrophobic specimen had a water contact angle of 154.3 ± 0.5°. The anti-icing, anti-corrosion and anti-wear properties of the prepared specimen were improved by approximately 70%, 110% and 160%, respectively. Moreover, the artificial surface could maintain its anti-icing properties even in the event of surface damage.
Abstract Herein, a superhydrophobic surface of AZ31B magnesium alloy prepared by high‐speed wire electrical discharge machining and modification with stearic acid is reported. The surface morphology and wettability of the superhydrophobic surface were investigated by scanning electron microscopy and optical contact angle measurement, respectively. A uniform micro‐/nanopetal‐like structure was shown within the superhydrophobic surface, resulting in a contact angle of 151 ± 0.5° and a sliding angle of 4 ± 0.5°. Notably, the superhydrophobic surface had better corrosion resistance than the bare magnesium alloy, and its corrosion current density was reduced by nearly one order of magnitude. Under both dry and wet friction conditions, the friction coefficient of the superhydrophobic surface was lower than that of the bare magnesium alloy surface, with a much lower wear loss. In addition, the friction coefficient of the superhydrophobic sample was lower than that of the bare magnesium alloy sample under both the dry and wet friction conditions. Thus, the superhydrophobic sample experienced reduced wear and had a low wear rate.
To improve the wear and corrosion resistance of aluminium alloys in salt environments, we produced superhydrophobic surfaces via high-speed electrical discharge machining. The specimens were characterised using a scanning electron microscope and a laser scanning confocal microscope and through contact angle (CA) measurement, measurement of electrochemical corrosion at an electrochemical workstation and wear testing. Results showed that the superhydrophobic specimens had a water CA of 151.5°. The corrosion of the as-obtained superhydrophobic specimens was significantly reduced by more than 50%, indicating their excellent anti-corrosion properties. The wear of as-obtained superhydrophobic specimens were reduced by approximately 10–35% in dry conditions and by approximately 45–85% in 3.5% NaCl solution, revealing their excellent anti-wear properties in both dry and salt environments.
Abstract This paper presents a method for measuring the thickness of the oxide layer on the surface of 7050 aluminum alloy based on image processing technology. As the 7050 aluminum alloy is oxidized to different degrees at different temperatures and different holding times, its surface color will also change significantly with the degree of oxidation. The image processing method was used to obtain the gray value of the sample photos with different degrees of oxidation, and the surface oxide layer of the sample was subjected to Ar + layer-by-layer sputter peeling. XPS analysis was performed on the peeled surface to calculate the thickness of the oxide layer. The oxidation was found. Relationship between layer thickness and gray value. The thickness of the oxide layer can be obtained by extracting the gray value of the surface of the test object. This measurement method has the advantages of low cost, non-contact, reliable measurement, convenient and fast.
This study offers a preliminary analysis of the impact of socioeconomic factors on rural labor migration between regions in China. Data were obtained from a 1994-95 survey on interregional migration among the rural labor force in 318 villages in 28 provinces, autonomous regions, and municipalities. The survey sample included 7677 households and 35,238 people. Findings are presented by age group: 17 years, 18-35 years, 36-59 years, and 60 years. The ratio of men to women was 3:1. More women were migrants in the 17 year age group. Younger migrants were better educated. Middle-aged migrants had better skills. Most people migrated after the Chinese New Year. Most migrants traveled with friends or relatives (47-74%). The proportion traveling through the arrangement of governmental institutions was small regardless of age (1-6%). About 1-2% made arrangements through private employment agencies. The elderly and middle-aged tended to leave the township but stay within the county. 22-35% left the county but not the province. Younger people tended to migrate outside the province. Large proportions of migrants aged 35 years traveled to cities, but cities also attracted middle-aged and elderly migrants. 23-37% traveled to coastal areas. Most stayed in the hinterlands. A large proportion of elderly migrants stayed longer than 10 months. Most found jobs through friends. Many were employed at state-owned institutions, but most worked in manufacturing and service industries and menial work. The largest proportion of elderly were engaged in own or township businesses. Younger migrants tended to comply with formalities involved in migration. In occupation selection, older migrants were concerned about job security, middle-aged migrants were concerned about income, and younger migrants focused on work friendships. The middle-aged had higher incomes.
Self-defense is such a kind of lawful means which is used by people to fight against law-breaking and crime. It is one of citizen's special rights, and also a mortal obligation. In order to apply this means effectively, use this special right correctly, and perform this obligation well, citizen must exactly master the composite condition of self-defense. Although our law has given a clear stipulation toward the composite condition of self-defense, judicial practice requires further perfection of legislation on it.
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