Introduction
The casting process directly produces the aluminum alloy that is used in the required parts. Ideal castability is required: good flowability, lower tendency to shrink, hot cracking and cold cracking, lower segregation and gas absorption. The element content of cast aluminum alloys is generally higher than that of corresponding deformed aluminum alloys, and most alloys have a near eutectic composition.
From 1905 to 1925, European and American countries conducted research on industrial aluminum alloys based on the study of phase diagrams of aluminum alloys. Aluminum-nickel alloys were initially investigated, but their castability was poor, so nickel did not become the primary reinforcing element. Later, studies were carried out on adding copper, magnesium, manganese, silicon and other elements to aluminum and achieved relatively ideal properties. Therefore, some binary and multi-component aluminum casting alloys were developed, including the famous silicon-aluminum alloy used around 1920. For the industry. [1]
Application
Cast aluminum alloys have good casting performance and can be processed into parts with complex shapes; they do not require much additional equipment; They have the advantages of saving metal, reducing costs and shortening working hours, and are widely used in the aviation industry and civil industry. Used to produce beams, turbine blades, pump bodies, pylons, wheel hubs, air intake lips and motor casings etc. It is also used to produce automobile cylinder heads, gears and pistons, instrument casings and compressor pump casings and other parts.
classification
Modern aluminum casting alloys can be divided into 4 series according to the main added elements, namely: aluminum-silicon series, aluminum-copper series, aluminum-magnesium series and aluminum-zinc series. For these four series, each country has corresponding alloy and alloy class markings. China adopts ZL+3 digit marking method. The first digit represents the alloy system, where: 1 represents the aluminum-silicon alloy system, 2 represents the aluminum-copper alloy system, 3 represents the aluminum-magnesium alloy system, 4 represents the aluminum-zinc alloy system and the second digit represents represents the aluminum-silicon alloy system. Three digits represent the serial number of the alloy. The table shows some typical aluminum casting alloys in China. According to the use characteristics of the alloy, they can be divided into: heat-resistant cast aluminum alloy, airtight cast aluminum alloy, corrosion-resistant cast aluminum alloy and weldable cast aluminum alloy.
Technology for refining aluminum alloys
Refining aluminum alloys mainly involves removing gases and non-metallic inclusions from the alloy liquid. The gas in the aluminum alloy is mainly hydrogen (more than 85%), and the inclusions are mainly aluminum oxide. Since the saturation solubility of hydrogen in liquid and solid aluminum alloys is almost twenty times different, the solidification process of aluminum alloys is easy to precipitate hydrogen, resulting in pinholes in castings. Inclusions and gases interact. In industrial pure aluminum, if the hydrogen content per 100g of liquid aluminum alloy is more than 0.1ml, pores will appear, while in high purity aluminum, every 100g of liquid aluminum alloy contains hydrogen. Once the volume reaches 0.4ml, pores will appear. It can be seen that degassing requires slag removal, and slag removal is the basis of degassing.
The commonly used refining agents for aluminum alloys are hexachloroethane or chlorine salts. This refining agent has very good degassing and slag removal effects, but is not conducive to environmental protection and is gradually being replaced by non-toxic refining agents. Domestic and foreign researchers have developed two types of effective refining methods, namely the rotating impeller method (RID method) and the flux injection method (FI method). In the rotating impeller method (RID method), inert gas is introduced into the alloy liquid, and the large bubbles are broken into small bubbles with a diameter of about 0.5mm by the rotation of the impeller and distributed evenly in the alloy liquid Can improve removal rate. gas effect; The flux injection method (FI method) consists of using powdered flux
