Effect Of Heat Treatment On Microstructure And Properties Of Er 5052 Aluminum Alloy

5xxx series aluminum alloy is a kind of non-heat treatable alloy, which is usually used in the conditions of hardening or annealing. It is widely used in aerospace, marine, automotive, construction, electronics, machinery manufacturing industry because of its low density, high strength, good corrosion resistance etc. In this paper, the alloy ingots were prepared by die casting, and cold-rolled sheets were prepared by homogenization, hot rolling and cold rolling. By means of tensile properties measurement, hardness testing, optical microscopy(OM), scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS), the microstructures and mechanical properties of alloys were investigated. The effect of annealing times and temperatures on microstructure and mechanical properties were systematically analysed and discussed based on the recrystallization kinetics and recrystallization nucleation theory. At the same time, the recrystallization temperatures of the alloys were confirmed.The results showed that, the obvious segregation phenomenon was in the microstructures of as-cast 5052 and 5052+Er alloys. 0.2wt.% Er addition did not act as the role of the grain refinement. After homogenization under 560℃ for 20 h, the phenomenon that grain boundary segregation of the experimental alloys was lost, the size and the number of the phases in grain boundaries were reduced, and the dendrite network became thin and discontinuous. The strip fiber organization was in the 4mm thick cold-rolling sheets. After intermediate annealing under 350℃ for 1h, the 5052 and 5052+Er aluminum alloys had been completely recrystallized.As the deformation of cold rolling increased, the grains were gradually elongated, and the tensile strength and the yield strength of the alloys increased, but the elongation of it decreased. The tensile properties of 5052+Er aluminum alloy were slightly higher than that of 5052 aluminum alloy. When the cold rolling deformation was 96%, The tensile strength, yield strength and elongation of 5052+Er aluminum alloy were 333 MPa, 321 MPa and 3.4%, respectively.The effects of annealing time and temperature on the microstructure and mechanical properties of the alloys were studied. The results indicated that the hardness(HV) of the 5052 and 5052+Er aluminum alloys showed typical "s" curve with the annealing time and temperature. The formulas to calculate the volume fraction of recrystallization, the JMAK recrystallization kinetics equation and recrystallization activation energy calculation formula were used for the recrystallization activation energies of the 5052 and 5052+Er aluminum alloys by linear regression analysis. The recrystallization activation energies of the 5052 and 5052+Er aluminum alloys were 118kJ/mol,143kJ/mol, respectively. According to the curves, the beginning and finishing recrystallization temperatures of 5052 aluminum alloy with 0.2 wt.% Er were about 265 ℃ and 300 ℃, separately. The recrystallization temperature of 5052 aluminum alloy with 0.2 wt.% Er was about 15℃ higher than that of the 5052 aluminum alloy. The reason was that the solid solution decomposed to form a dispersion of secondary Al3 Er, which could pin the dislocations strongly and impede grain boundaries to move. So it made the recrystallization temperature of 5052 aluminum alloy higher.The effects of annealing temperature on the tensile mechanical properties, the distribution of secondary phases and intergranular corrosion properties were investigated. The results showed that, with annealing temperature and time increasing, the tensile strength and yield strength of the alloys increased, elongation of it decreased, the fracture nests of the specimens were larger and deeper, and the tearing edges were less and more fine. The effects of annealing temperature on the number, the distribution and the morphology of second phases were not significant. These particles mainly contained Al, Fe, Er. With the increase of annealing temperature, the weightlessness of the alloys after corrosion increased. The weightlessness of 5052 aluminum alloy with 0.2wt.% Er was higher slightly. The weightlessness of the alloys in different conditions were in the range of 3.0~3.6mg/cm2. After the intergranular corrosion, corrosion phenomenon had not been found in the appearance and the microstructure of the alloys. Because of low content of Mg, the intergranular corrosion resistance of the alloys was very good, and Mg was solute in matrix and β phase did not precipitate at the grain boundary.