Investigation On The Melt Treatment And Homogenization Of LC4 Aluminium Alloy

LC4 aluminium alloy is one of super-strength aluminium alloys which has been widely used in aviation and national defence industries in our country. To further improve its properties by proper treatment has great value both in practice and theory.In this paper, the effects of melt treatment (including the four-factor-purification and melt superheating treatment) and homogenization on the microstructure and properties of LC4 aluminium alloy were investigated. The mechanism of melt superheating treatment was also analyzed. The optimum mechanical properties were obtained through a process of homogenization with the suitable temperature and time.The experimental results show that the effect of superheating temperature on the secondary dendrite spacing is unnoticeable when the LC4 aluminium alloy is superheated in the temperature range of 720℃～1020℃. The secondary dendrite spacing is relatively small in the sample superheated to 960℃. Dendrite nets become well-distributed with the increase of superheating temperature. With the increase of superheating temperatures, the grain size of LC4 aluminium alloy, treated with the four-factor-purification, grows obviously, with the grain size goes down to the minimum when superheated at 780℃, whereas the grain size of LC4 aluminium alloy, without the treatment of four-factor-purification, changes indistinctly and is relatively small when superheated at 840℃. The secondary dendrite spacing grows markedly with the increase of holding time in the range of 15min～60min, but the effects on dendrite nets and grain size are not obviously. Because the grain size of LC4 aluminium alloy with the treatment of four-factor-purification is less than that without the treatment, the temperature of superheated should be lower than 800℃ in order to maintain the advantage of four-factor-purification treatment. By the aid of optical microscopy and tensile test, it shows that the four-factor-purification treatment is helpful to improve the strength and the ductility of LC4 aluminium, and the optimum mechanical properties could be obtained through a suitable process of homogenization. After homogenized at 468℃ for 48h, the ultimate strength of LC4 aluminium alloy reaches 272 MPa, with the yielding strength 183 MPa and elongation 19.0%.