Smelting of cast non-ferrous alloys
1 cast aluminum alloy Aluminum alloy performance and application Cast aluminum alloys have a lower density than cast iron and cast steel, but have a higher specific strength. Therefore, the use of aluminum alloy castings under the same load conditions can reduce the weight of the structure, so aluminum alloy castings are widely used in the aviation industry and power machinery and transportation machinery manufacturing. Aluminum alloy has a good surface gloss and good corrosion resistance in the atmosphere and fresh water, so it has a wide range of applications in the manufacture of civilian utensils. Pure aluminum has good corrosion resistance in oxidizing acid media such as nitric acid and acetic acid, so aluminum castings have certain applications in the chemical industry. Pure aluminum and aluminum alloys have good thermal conductivity, heat exchange devices used in chemical production, and parts requiring good thermal conductivity on power machinery, such as cylinder heads and pistons of internal combustion engines, etc. Manufacturing. Aluminum alloy has good casting properties. Since the melting point is low (the melting point of pure aluminum is 660.230C, the casting temperature of aluminum alloy is generally about 730-750oC), casting methods such as metal type and pressure casting can be widely used to improve the intrinsic quality, dimensional accuracy and surface of the casting. Smoothness and productivity. Due to the large latent heat of solidification, the solidification process of aluminum liquid lasts much longer than that of cast steel and cast iron under the same weight conditions, and the fluidity is good, which is beneficial to casting thin-walled and complex castings. Classification, grade of casting aluminum association Aluminum alloys are divided into two categories according to the processing methods, namely, pressure-processed aluminum alloys and cast aluminum alloys (represented by YL and ZL, respectively). In the cast aluminum alloy, it is divided into four series according to the main alloy elements added, namely cast aluminum silicon alloy, aluminum alloy copper alloy, cast aluminum magnesium alloy and cast lead zinc alloy (ZL1X X, ZL2 XX, respectively). ZL3 XX and ZL4 XX), in each series, are divided into several grades according to their chemical composition and performance. Table 3 lists the grades of several aluminum alloys included in the National Standard for Cast Aluminum Alloys. Table 3 Grades of cast aluminum alloy No. Alloy grade Alloy code No. Alloy grade Alloy code No. Alloy grade Alloy code 2 cast copper alloy Cast copper alloy is a cast alloy material widely used in industry. Copper-based alloys are widely used in the shipbuilding and chemical industries because of their good resistance to fresh water, seawater and certain chemical solutions. Copper-based alloys are also commonly used in the manufacture of sliding bearing bushings for heavy-duty and high-speed running shafts on various machines due to their good thermal conductivity and wear resistance. Cast copper alloys fall into two broad categories, namely brass and bronze. Brass is a copper alloy with zinc as the main alloying element. In cast brass, manganese brass, aluminum brass, silicon brass, lead brass, etc. are formed by adding other alloying elements. In copper alloys, zinc is not commonly used as an additive element, such as tin bronze, aluminum bronze, lead bronze, beryllium bronze, and the like. In the national standard, there are 9 kinds of cast copper alloys, and 29 grades are counted. 3 other non-ferrous alloys In addition to cast aluminum alloys and cast copper alloys, there are many types of cast non-ferrous alloys. Among them, cast magnesium alloys, cast titanium alloys and cast zinc alloys are commonly used. Magnesium alloys and titanium alloys are mostly used in the aerospace industry due to their high specific strength. Among them, titanium alloy also has strong corrosion resistance to a variety of corrosive media, so it is also used in the manufacture of castings subjected to corrosion on petrochemical equipment. Zinc alloys are widely used in the manufacture of thin-walled and structurally complex castings because of their relatively high strength and excellent casting properties. Zinc alloy has good casting properties, strong filling ability and no hot cracking, so it is especially suitable for metal type and pressure casting. Pressure casting methods are commonly used in mass production to produce thin-walled and complex zinc alloy castings. 4 Casting of colored alloys
1 ZALSi7Mg ZL101 10 ZALSi12 Cu1Mg1Ni1 ZL109 19 ZALCu5MnCdA ZL204A
2 ZALSi7MgA ZL101A 11 ZALSi9Cu2Mg ZL111 20 ZALCu5MnCdVA ZL205A
3 ZALSi12 ZL102 12 ZALSi7Mg1A ZL114A 21 ZALR5Cu3Si2 ZL207
4 ZALSi9Mg ZL104 13 ZALSi5Zn1Mg ZL115 22 ZALMg10 ZL301
5 ZALSi5Cu1Mg ZL105 14 ZALSi8MgBe ZL116 23 ZALMg5Si1 ZL303
6 ZALSi5Cu1MgA ZL105A 15 ZALCu5Mn ZL201 24 ZALMg8Zn1 ZL305
7 ZALSi8Cu1Mg ZL106 16 ZALCu5MnA ZL201A 25 ZALZn11Si7 ZL401
8 ZALSi7Cu4 ZL107 17 ZALCu10 ZL202 26 ZALZn6Mg ZL402
9 ZALSi12Cu2Mg ZL108 18 ZALCu4 ZL203
In the casting method, in addition to sand casting, copper alloys and other non-ferrous alloys also widely use various special casting methods such as metal casting, centrifugal casting, low pressure casting and graphite casting.
In the copper alloy casting, the metal casting method is adopted to accelerate the solidification of the alloy, which plays an important role in improving the quality of the casting and reducing the casting defects. Metal-type casting can subdivide grains (especially for aluminum bronze and manganese brass), reduce pores, improve the mechanical properties and air tightness of the alloy (especially important for tin bronze), in high-lead copper alloys such as lead bronze, Casting in a metal type (and water-cooled metal type) prevents segregation of copper components. Further, since there are many cylindrical parts (bearings, bushings) and the like in the copper alloy castings, centrifugal casting methods are often used. In addition, large cast copper parts (such as large marine propellers) can also be used in low pressure casting methods to increase the density of the alloy and reduce inclusions in the casting process. Some copper alloys (such as lead brass) can also be pressure cast.
Magnesium alloys are poor in casting properties, especially in thermal cracking. Therefore, most magnesium alloy castings are still sand-cast, and only a small part of the shape is simple casting, which can be cast in metal form. The pressure casting method is rarely used in magnesium alloy casting.
Titanium alloys are extremely chemically active. During the casting process, the titanium liquid interacts with most of the mold materials (including various types of sand and steel), causing the castings to be contaminated, so only special casting materials can be used. Casting such as yttria or graphite.
The smelting process has a large impact on the performance and defects of non-ferrous alloy castings. Most non-ferrous alloys are prone to pores and inclusions, especially titanium alloys, aluminum alloys, magnesium alloys and certain copper alloys. The general smelting process is:
1) According to the alloy grade specified in the technical requirements of castings, the chemical composition range of the alloy can be detected, and the chemical composition is selected from them;
2) According to the burning rate and composition requirements of the elements, the batching calculation is carried out, and the amount of various charging materials is obtained, and the charging material is selected. If the charge is contaminated, it needs to be treated to ensure that all the charge is clean, free of rust, and preheated before feeding;
3) Inspect and prepare utensils, paint and preheat to prevent contamination of gases, inclusions and harmful elements;
4) Feeding. Generally, the order of feeding is: returning charge, intermediate alloy and metal material, metal material with low melting point and easy oxidation, such as magnesium, added after melting of the charge;
5) In order to reduce the inhalation and oxidation pollution of the alloy liquid, it should be melted as soon as possible to prevent overheating. If necessary, some alloy liquids must be protected with a covering agent;
6) After the furnace material is melted, refining treatment is performed to purify the alloy liquid, and the refining effect is checked;
7) Perform metamorphic treatment and subdivision tissue processing as needed to improve performance and verify treatment effects;
8) Adjust the temperature and carry out the pouring. Some alloys are agitated before casting to prevent specific gravity segregation.