The rapid growth of global aluminum production needs the substantial growth of alumina. The global bauxite resources are abundant, and the mining life is as high as 250 years. However, due to the uncertainty of the market information of the rapid growth of electrolytic aluminum, the large-scale expansion projects of alumina abroad are still slow, and the market supply cannot be fully guaranteed in the past year or two, resulting in the rapid change of global alumina supply and demand. In 2003, the global alumina output reached 54,767,300 tons, with a year-on-year increase of 6.6% and consumption of 5,464. After the balance of supply and demand in the global market in that year, the surplus fell to 127,300 tons. According to the data of International Aluminum Association (IAI), in the fourth quarter of 2003, the output of alumina in the world's major alumina producing areas increased compared with the same period of last year, but the global alumina market supply was still very short in the fourth quarter of last year. From the current overall situation, with the expansion of global electrolytic aluminum production capacity, especially in China, the demand for alumina will maintain a very strong momentum.

At present, the world's alumina production capacity has become quite tight. There are nearly 30 countries producing alumina in the world, and the world's alumina smelters have used nearly 100% of the production capacity, and there is almost no idle capacity to be re-used. At this stage, no new projects have been put into production except China. The bankruptcy protection of Caesar Aluminum Factory in the early stage has made the original shortage of alumina supply even more tense. It is estimated that the shortage of alumina supply will further deteriorate in the next year or two.

Due to the shortage of imported aluminum plates in the domestic market, the price of alumina in the international market has been high. Since the beginning of 2003, the price of alumina has been rising all the way. At present, the import price of spot alumina has risen to $520-$530 per ton, while the warehouse delivery price of imported alumina for immediate delivery in China port is about RMB 5,200-5,400 per ton. Chinalco, an alumina producer in Z, China, has also raised the price of alumina to RMB 4,300, an increase of. It is estimated that the price of alumina will continue to climb in 2004-2005, possibly reaching a record of $600/ton. According to the alumina price of $500/ton, even if other factors remain unchanged, the production cost of primary aluminum is at least $1,650/ton.

The continuous rise of alumina price has made producers start to redistribute production and capacity. In the next few years, alumina production will increase rapidly. It is predicted that alumina production will increase by 22% to 68.516 million tons in 2006, in which the share of Asia's total alumina production will increase from 18% last year to 24%, while that of Australia will decrease from 27.5% to 26.2%. It is predicted that the global alumina supply will be tight.

Composite hard anodic oxidation and wear resistance of 6063 aluminum alloy

Experiment on machinability and wear resistance of imported aluminum sheet

Aluminum and aluminum alloys have high specific strength, excellent processability and corrosion resistance, and their applications in various industries are increasing. Surface treatment can improve the bearing capacity and wear resistance of aluminum and aluminum alloys, and it plays a very important role in the production of aluminum and aluminum alloy components.

Hard anodizing is a common and effective surface treatment method for aluminum and its alloys. In order to improve the surface hardness and wear resistance of aluminum, a thick Al _ 3O4 layer is formed on the aluminum surface by electrochemical method. In order to further improve the performance of the coating, second phase particles can be introduced into the coating. Generally speaking, such particles can be divided into two categories: hard particles and soft particles. Hard particles, such as SIC and SiN, can increase the hardness of the coating; Soft particles, such as polytetrafluoroethylene (PTFE) and MOS2, can increase the self-lubricating properties of the coating.

In this paper, the composite hard anodic oxidation of aluminum alloy with PTFE particles was studied experimentally, and the friction coefficient of the composite anodic oxidation layer was measured, and the results were compared with those of the conventional hard anodic oxidation layer.

Test method

The aluminum alloy for anodic oxidation is 6063 alloy in T4 state, and its chemical composition (mass fraction/%,the same below) is shown in Table Anodized samples are wafers with a diameter of 30 mm x 5 mm. Before oxidation, the samples were polished with diamond gypsum, and the surface roughness was Ra0. 2~0。 3µm。

Chemical composition of 6063 aluminum alloy

Si Fe Cu Mn Cr Zn Ti Al

0.45 ~ 0.900.20 ~ 0.600.350.100.100.100.100.10 Balance

Generally, the hard anodic oxidation solution is H2SO4 solution with a concentration of 2. 24 mol/L, and the composite anodic oxidation solution is a mixed solution of the above-mentioned conventional hard anodic oxidation solution, a polytetrafluoroethylene dispersion, with a mixing ratio of 224 mol/lhjs (1 aqueous solution: polytetrafluoroethylene dispersion = 3: 1). The temperature of the oxidizing solution is controlled by the annular cooling tube placed in the oxidizing swabs. The whole oxidation process adopts constant temperature oxidation at -3℃~-4℃. During the oxidation process, the oxidizing solution is stirred with a magnetic rod, and the lead plate is used as the cathode, and the cathode area is more than 10 times that of the anode. Self-flowing power supply is used for oxidation power supply, and the stable oxidation current density of anode is 2.5 A/dm:.

The hardness of the oxide layer was measured by an automatic microhardness tester, and the measuring position was the outer surface of the oxide layer. The applied load was 100g and the loading duration was 8s, and the cross-sectional morphology of the oxide layer was observed by an optical microscope.

In order to characterize the friction performance of the composite hard anodic oxide layer, the friction torque measurement test under dry friction condition at room temperature was carried out with MM-200 wear tester, and the slide block device was used in the test, as shown in Figure]. At this time, the composite hard anodic oxidation sample is processed into a cuboid with the size of 20 mm× 10 mm× 5 nun as a fixed test rod; The rotating sample is a quenched GCr15 steel ring with an outer diameter of 16mm and a thickness of 10mm. The hardness is 60HRC and the surface finish is Ra0. 2µm。 Before the test, both the fixed sample and the rotating sample were carefully cleaned with chemically pure liquor semen. The friction torque is measured by step loading method: the initial load is 49 N, and then the load is increased by 49 N every time until it reaches 196 N；; The test time under each load is 5 minutes. The rotating speed of the rotating test bar is 100 r/rain, and the relative sliding speed at the contact point between the fixed sample and the rotating sample is equivalent to 0. The friction factor of 21 m s-1 is obtained by dividing the friction torque directly measured by the test by the used load and the radius of the rotating sample.

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