Study On Semi-Solid Powder Rolling Of 2024 Aluminum Alloy Strips

As a novel alloy strip forming method, semi-solid powder rolling combines semi-solid processing with powder rolling. The process has a short procedure, near-net shape forming, low energy consumption, etc. Strips prepared by this method have high density, homogeneous microstructure and fine grain size. At present, semi-solid powder extrusion has been used in alloy and composite materials, etc. but there’s still no report about the study of semi-solid powder rolled 2024 aluminum alloy strips. In this work, semi-solid powder rolling was used to prepare 2024 aluminum alloy strip. Hot rolling was used to make the strips densification. In order to improve the mechanical properties of the hot rolled strips, heat treatment was also optimized. The main results are as follows:The strips’ forming ability is affected by the liquid friction seriously. When the liquid friction is too low, the porosity is high and powders combine poorly. It is difficult to rolling the strip continually when the liquid friction is too high. The rolling force is much lower than solid rolling at 25℃.With the powder heating at 585℃ for 40 min, the rolling force is only 1/3of solid powder rolled at room temperature. As the temperature increasing, the rolling force reduces little. Strip density and micro-hardness increase with the increasing temperature. Original particle boundary disappeared with isometric microstructure. The grain size of 10.68 um is much smaller than the casting microstructure. At the same time, some second phases are around the grain boundary. The oxide films of powder particles are also broken, A part of the oxide is piled into matrix as a reinforcing phase with a good bonding with the matrix. Other parts gather at in the grain boundary with second phase. Coupled with not full dense strip, the mechanical property is poor. The best semi-solid powder rolling parameters is heating at 585℃for 40 min. The micro-hardness, tensile strength, yield strength, elongation and relative density are 83 HV, 128 MPa, 105 MPa, 3.1%and 93.7%.During the densification of strips, density increased quickly when the deformation extent is less than 40%.As the deformation extent increasing continually, density increased little, strength is constantly improved. The best hot rolling temperature is 450 ℃. After 75% hot deformation extent, the original coarse phase around the grain boundary disappeared. The oxide also spread evenly. The micros-hardness, tensile strength, yield strength and elongation, respectively are 149 HV, 395 MPa, 308 MPa and 12.1%.As the solution temperature increasing, the micro-hardness increase at first, then decrease. It has also the same trend with the solution time increasing. At 180 ℃ ageing 12 h, the main precipitate phases are Cu Al2, Al2 Cu Mg.There is also a small amount of dispersed oxide. The best heat treatment process is solution treatment at 490℃for 45 min, aging at 180℃for 12 h. The micros-hardness, tensile strength, yield strength and elongation are 223 HV, 526 MPa, 449 MPa, 11.3%. Fracture mechanism of strips is ductile fracture.