Asked the melt casting aluminum alloy ZL301 instrument cover process design

Introduced the characteristics of aluminum alloy investment casting, aluminum alloy investment casting commonly used gypsum-type investment casting and ceramic-type investment casting process, casting aluminum alloy refining, metamorphosis, refining process and aluminum alloy liquid filtration and purification technology. Keywords: investment casting? aluminum alloy? Filtering purification classification number: TG146.2;TG249.5?Literature identification code: B?Article number: 1001-2449(2000)06-0048-03?In recent years, in the world casting of the composition of the emergence of a striking trend, that is, aluminum alloy casting of the production of rapid growth. As aluminum alloy has a series of excellent characteristics such as low density, high strength, widely used in aviation, aerospace, automotive, machinery and other industries, especially in the automotive industry, in order to reduce fuel consumption, improve energy efficiency, product design is increasingly taking into account the lightweight, aluminum alloy castings instead of steel, iron castings, will be the long-term development trend. With the domestic and foreign aviation, aerospace, automotive, shipping, machinery, electronics and other industries used in the structure of parts to large, thin-walled, complex, whole, lightweight direction, so that the aluminum alloy precision casting technology has developed rapidly. 1 aluminum alloy investment casting characteristics [1] 1.1 can make large, thin-walled, complex castings at present, the developed countries can produce large-scale electronic equipment frames, shells, and other aluminum alloy precision castings. Aluminum alloy castings, such as the largest size up to 800 ~ 1000mm, wall thickness is generally 1.5 ~ 2.0mm, local only 0.75mm, size tolerance of ?0.125mm/25mm.1.2?Castings surface quality is excellent precision thin-walled aluminum alloy casting surface roughness is generally required to be strict, its Ra ?0.8 ~ 3.2?m.1.3?Can be a complex, thin-walled components to provide integral molding technology parts by the complex structure, thin-walled parts. Components to provide integral molding technology parts by machining and then welded into a combination of parts, so that the complexity of the parts is limited, surface roughness increases, manufacturing costs rise. And the use of precision casting technology can make the structure of very complex parts and components of a molding. Such as Boeing 767 aircraft on the fuel booster pump shell castings, by 22 wax molds were pressed and then combined into 4 combination of wax molds, and then the 4 combination of wax molds assembled into a booster pump shell the whole wax molds, mixed with gypsum slurry infused into a gypsum type, casting in a vacuum into the casting. 1.4 can significantly improve the utilization rate of the material by forging blanks machined parts need to be cut out of a large amount of metal, resulting in a great waste of metal materials. Great waste of metal materials. If the whole precision castings instead of machined and then combined parts, it will greatly improve the utilization rate of materials, thereby significantly reducing the manufacturing cost of products. 1.5 can greatly shorten the product development and production cycle, such as the U.S. cruise missiles AGM-89B, the body of the bomb with 9 large-scale castings instead of 44 aluminum precision die forging, machined parts welded together into a combination of parts, so that the missile manufacturing man-hours saved 75%, manufacturing costs reduced by 30%. 1.4 can significantly increase material utilization rate by forging blanks formed by machining of parts require removal of a large amount of metal, resulting in a great waste of metal materials. Aluminum alloy casting process 2.1 melting mold production of aluminum alloy melting point is low, pouring temperature is low, surface tension is large, aluminum alloy liquid surface is easy to form an oxide film, so the aluminum alloy liquid on the casting wall of tiny holes on the replication ability is poor, the wall of the tiny bumps or inclusions in the casting will cause a large dent. Therefore, the nature of the mold material and the surface quality of the wax mold has a great influence on the surface roughness of aluminum alloy castings. Paste molding materials do not reproduce wax molds with low surface roughness even on the surface of the press. In order to produce a low surface roughness of the molten mold, the liquid molding material with low viscosity and strong mold-covering ability should be used for high-pressure injection molding. The inner cavity of the complex castings, the inner cavity of the mold can be used water soluble core molding. 2.2 gypsum type mold casting gypsum type of good reproducibility, can obtain high dimensional accuracy, low surface roughness of the castings; gypsum type of low thermal conductivity, at the same time is a hot mold casting, so can be poured out of ceramic-type fine casting casting wall thickness thinner than the casting [2], conducive to the thin-walled casting in the pressure of the crystallization of the solidification, can be poured out of the wall thickness of the thin wall of the uneven Precision castings without shrinkage and shrinkage holes. Therefore, gypsum type investment casting is mainly used for casting large, thin-walled, complex, whole aluminum alloy precision castings. According to the water-powder ratio of gypsum-type mixture, quantitative tap water into the container, and then the powder evenly sprinkled into the water mixing 2~5min, the best mixer and mold box set with the same in the vacuum chamber, mixing and grouting are carried out in a vacuum, can effectively prevent the gypsum-type bubbles, hold air, pouring insufficient defects. In order to stabilize the process and ensure the quality, the water temperature of mixing should be controlled in a certain range, and other liquid additives such as n-octanol should be dissolved in water and added together when adding water. The plaster should be left for 24h after solidification and before dewaxing, so that the plaster can harden sufficiently. For pulling mold gypsum type, after pulling mold can be directly baked without dewaxing, because there is no residual wax in the type, gypsum type baking temperature up to 250~400? can be, in order to remove free water and water of crystallization. For molten mold gypsum type, in order to dewaxing penetrate into the gypsum type of residual wax burned out, should be baked to 650 ~ 750? Because of the poor permeability of gypsum type, it is appropriate to use vacuum pouring, negative pressure or centrifugal pouring. 2.3?Ceramic shell investment casting using the traditional ceramic shell investment casting method, through the improvement of the process can be manufactured complex medium and small aluminum alloy investment castings. Due to the aluminum alloy mold castings thin wall, low strength, casting can only be gently knocked through the pouring system method of shell. However, aluminum alloy pouring temperature is low, density is small, the dynamic pressure and static pressure generated when pouring and thermal shock are small. Therefore, the shell is required to have high wet strength, good air permeability, appropriate high-temperature strength and low residual strength. In order to reduce the residual strength of the shell, the following measures can be taken [3]. (1) Selection of lower viscosity, bonding strength of the binder, such as the use of ethyl silicate hydrolysate may be more favorable than silica sol. (2) Reduce the shell level. (3) Increase the degree of reinforcement layer sand. (4) reduce the shell baking temperature, add additives such as oxidizer or latex in the shell coating, so that the shell baking temperature, shell high temperature strength and residual strength to reduce, improve the collapse of the shell and permeability. 3 aluminum alloy melting process melting process is an important link in the production of aluminum alloy castings, aluminum alloy melting not only to ensure that the alloy's chemical composition of the qualified and uniform and to a large extent determines The casting organization of the degree of density and mechanical properties, this should be strictly controlled alloy melting process. 3.1 casting aluminum alloy refining aluminum chemical properties are more active, melting process is easy to react with the water, oxidation and hydrogen absorption. Hydrogen in the liquid and solid aluminum alloy in the saturated solubility difference of nearly 20 times [4], so aluminum alloy castings are prone to pinholes, inclusions and other defects. The purpose of refining is to remove the gas and non-metallic inclusions in the aluminum alloy liquid. Aluminum alloy gas is mainly hydrogen (accounting for more than 85%), inclusions are mainly aluminum oxide. Inclusions and gases are interacting with each other, it has been measured that when the content of impurities in the aluminum alloy liquid is 0.002% and 0.2%, the corresponding hydrogen content per 100g of aluminum alloy liquid is 0.2ml and 0.35ml, in the high-purity aluminum per 100g of aluminum alloy liquid containing hydrogen as high as 0.4ml, there will be a porosity, and in the industrial pure aluminum per 100g of aluminum alloy liquid containing hydrogen is only 0.1mg, there will be pores, when the content of impurities in the alloy liquid <0.001%, even if the amount of hydrogen per 100g of aluminum alloy liquid up to 0.3ml will not appear pinhole [5]. It can be seen that in addition to the gas must be removed from the slag, slag removal is the basis for the removal of gas. Reduce environmental pollution and reduce production costs is the direction of the development of aluminum alloy refining technology [6], currently used at home and abroad refining methods are such or such shortcomings, domestic and foreign researchers have developed two types of effective refining methods, namely, the rotating impeller method (RID method) and the spray melt method (FI method), the RID method is used in the smaller melting amount of aluminum alloy refining treatment, the test proved that the RID method of hydrogen removal efficiency is better than the traditional single-tube method. RID method is used for refining aluminum alloys with small melting volume, and the test proved that the efficiency of RID method is 3 times higher than that of the traditional single-tube gun blowing method. The melt spraying method appeared in the early 80's, and soon attracted people's attention, the refining treatment effect is better than the traditional melt method. Rotary impeller method and melt injection method principle, characteristics and scope of application are shown in Table 1 [7]. Table 1?Principles, characteristics and scope of use of the rotary impeller method and the melt injection method refining method working principle technical characteristics scope of use of the melt injection method (FI method)? Powdered flux to inert gas as a carrier uniformly sprayed into the alloy liquid, increasing the contact area of the flux and the alloy liquid to enhance the role of slag removal, while the flux to change the nature of the interface between the bubbles and the alloy liquid to improve the effect of inert gas in addition to hydrogen? Refining effect is good, short time, processing 5~10min, 100g of hydrogen content in the melt can be reduced to 0.06ml, less dosage of flux, less harmful to human body, low processing costs, easy to operate, stable quality, the use of dry flux, small loss of aluminum? It is suitable for the molten liquid treatment with strict requirements of degassing and slag removing and one-time completion of refining and deterioration or refinement of the rotating impeller method (RID method). Through the impeller rotating cutting large bubbles broken into small bubbles with a diameter of about 0.5mm, they are uniformly distributed in the alloy liquid, slowly rising, can improve the effect of degassing, in order to improve the role of slagging in the inert gas nitrogen and argon, add 5% to 10% of chlorine or freon and other active gases (rotating impeller speed of 300-500r/min)? In addition to the high efficiency of the gas, 100g of molten hydrogen content can be reduced to 0.06ml, inert gas does not pollute the environment, does not cause alloy burns, and low processing costs, process parameters are easy to control, good reproducibility. The disadvantage is that the impeller made of graphite is easy to damage, low life? Applicable to a variety of alloys, especially containing magnesium, sodium, strontium and other easy to burn elements of the alloy 3.2 casting aluminum alloy metamorphosis and grain refinement 3.2.1 metamorphosis treatment A-lSi alloy metamorphosis treatment is usually used in the pure metal, intermediate alloys and melts three kinds of ways. Sodium metamorphosis is generally used in the form of melt, Sr, Sb, Te, RE and other metamorphism is generally used in the form of pure metal, Sr, RE is also added in the form of intermediate alloys or melts. In recent years, the development of Na-Sr, Sr-RE and other composite metamorphic agents, achieved better results. Such as the use of w (RE) = 0.2% and w (Sr) = 0.04% composite metamorphic agent on the ZL101 alloy metamorphic treatment to obtain a separate w (Sr) = 0.08% of the metamorphic effect [8], and at the same time reduce the casting of the tendency of the pinhole, the use of Na-Sr composite metamorphic not only solved the problem of the short period of validity of the Na metamorphic, but also solved the problem of the latent period of Sr metamorphic. 3.2. 2 grain refinement since the 40s people have found in aluminum alloys in the addition of trace titanium and boron can greatly refine the grain, so that the first crystal? -Al from coarse dendrites into fine isometric crystals. At the same time, it can improve the shrinkage capacity of the alloy, reduce the tendency of thermal cracking, reduce the size and number of pinholes, make their distribution more diffuse, and improve the chemical and electrochemical properties of the alloy and the surface quality. Currently used at home and abroad the role of grain refining agent characteristics and scope of application of the table 2? Various grain refining agent role characteristics refining agent role characteristics of the amount added / % of the applicable alloys titanium (Ti) Al3Ti, TiC can be used as a foreign nuclei, so that grain refinement, A-lCu system alloy refining effect is better, the size of the grains can be reduced from 1 to 3mm to 0.2 ~ 0.5mm0.1~0.15 ZL101A, ZL114A, etc. 0.2 ~ 0.25ZL201, ZL201A, etc. titanium boron (Ti + B) Al3Ti, TiB2, AlB2 can be used as the nucleus of the grain, refining effect and resistance to recession than the ability to add titanium alone is good, intermediate alloys in the titanium and boron mass ratio of 5 is usually, and salt refining agent in the 7 ~ 10Ti: 0.25B: 0.005 ZL205ATi:0.05B:0.01ZL101A,ZL105AZirconium (Zr)Al3Zr as a non-spontaneous nuclear grain refinement, the role of the A-lMg alloy is stronger than Ti 0.1~0.15ZL301,ZL205A, etc. 4 filtering and purification technology in recent years, more than a decade, alloying liquid filtration and purification technology in the domestic and foreign casting production has been widely used, the use of ceramic filters or hardening of the alloy. The use of ceramic filters or hardened glass fiber filter [9], to remove inclusions in the alloy, improve the mechanical properties of castings, processing performance, performance and improve the casting pass rate is very significant. Aluminum alloy liquid filtration purification can be used flexible glass fiber mesh, will be put into the shell gating cup or put into the shell straight casting channel, can effectively remove non-metallic inclusions in the aluminum liquid, and significantly reduce the sand holes, porosity, slag eyes and other defects, improve the performance of the alloy, so the filtration and purification technology has been more and more widely used in aluminum alloy investment casting. 5?Conclusion? Language aluminum alloy investment casting technology is one of the advanced manufacturing technology near net shape, with the aluminum castings in the national economy demand increases, in the 21st century will get more rapid development. We should improve the quality of raw and auxiliary materials for aluminum alloy investment casting, large-scale thin-walled complex aluminum alloy precision casting overall forming technology, aluminum alloy melting quality furnace detection technology, aluminum alloy pouring and filling technology and other aspects of the research, in order to improve China's aluminum alloy investment casting technology level, and to promote the industry's technological progress. Reference? Reference? Text? Ye Rongmao, Wang Huiguang, Tian Jing. Nonferrous alloy thin-walled precision castings casting process development and characteristics. Special Casting and Nonferrous Alloys,1995(2):33~342?Tan Derui,Chen Meiyi. Art casting. Shanghai: Shanghai Jiao Tong University Press, 1996.3 Jiang Yuhua. Technical ways and methods to improve the quality of aluminum alloy ceramic shell investment castings. National Symposium on Theory and Technology of Investment Casting, Weihai, Shandong, 1994.4 Xiong Yancai, Huang Zhiguang, Wang Wenqing. Research and progress of direct determination of hydrogen content in aluminum and aluminum alloys. Special Casting and Nonferrous Alloys, 1995(4):12~155. Kang Jixing, Fu Gao Sheng. Behavior of inclusions and gases in aluminum melts. Special Casting and Nonferrous Alloys, 1995(5):5~86. Yang Changhe. Aluminum liquid dehydrogenation purification technology for the 21st century. Special Casting and Nonferrous Alloys, 1999(Supplement):109~1117?Aeronautical Manufacturing Engineering Handbook. Beijing: Aviation Industry Press, 1994.8?Li Peiyong, Jia Jun, Guo Jingjie. Research progress of melt treatment of sub***crystalline A-lSi alloys. Special casting and non-ferrous alloys, 1997(2):36~399?Chen knitting Caizhong, She Zhizhong, Zhou Shanmin et al. Steel fine casting filtration technology research. Special casting and non-ferrous alloys, 1998(1):18~21