| 5XXX series aluminum alloys are ideal materials in automobile industry becauseof its small specific gravity, high specific strength, good corrosion resistance, wellweldability and easy shaping etc. With the rapid development of transportation industryin our country, the demand for aluminum sheets grows day by day. Compared withforeign advanced level, however, the quality of5xxx Al-alloys has gap. The outstandingproblem comes to be its nonuniformity of deformation which is closely related tostructure uniformity.At present, there are no systematic research on the homogenization process ofaluminum alloys. In fact, homogenization process has tremendous influence on thehomogeneity of structure and deformation of aluminum alloys. So it is necessary toresearch on the homogenization process for each of alloys.5052aluminum alloy is one of the most widely used products in5XXX seriesaluminum alloys. in this paper, the test alloys are5052and5052micro-alloyed with Erand Sr respectively. The microstructures and properties of5052、5052+Er and5052+Srwhich are treated by different homogenization rules were researched by OM、DSC、SEM、TEM、EDS and Vickers hardness etc. Uniform structures of5052aluminumalloys were expected.5052+Er alloy after typical homogenization process were rolledand we also test the properties of the sheet.The results show that, the microstructure of as-cast5052、5052+Er and5052+Sralloys consist of α-Al and iron-rich phases which is acicular or Chinese charactersshaped. The size of second phase is more than100μm. The dendritic segregation isobvious in the cast structures.There are two existence forms of Er in5052: one is insolution, and the other form is Al3Er, which can refine the structure and purify the melt.After different rules of one-stage homogenization, we have the followingconclusions: when the homogenization temperature is under500℃, thedendriticsegregation do not eliminate completely. With the increase of homogenizationtemperature and time, non-equilibrium phases of as-cast alloys tapered. Whenhomogenization temperature is up to560℃, the structure of as-cast alloys improvesignificantly. We found the coarse second phases after the temperature was up to575℃.After homogenization at590℃for6h, there is a large number of over burning structures in5052and Sr-additional alloys. So in this paper,560℃is more appropriatefor improving the microstructure.We also studied the influence of holding time on the homogenization process.Asthe homogenization time rose from12h to30h, the second phase in the alloy found nocoarsen. So we think that30h is appropriate time for homogenization.In the experiments, the cooling mode we used are furnace cooled and air cooledrespectively, and the result showed that there is significant influence between these twocooling way. More precipitates can be obtained when using furnace cooled mode, andthe microstructure become more uniform. Which indicate that it’s more conductive toprecipitates when using furnace cooled.We also research the different two-stage homogenization of the three alloys and gotthe optimized program which are560℃/30h+150℃/10h and560℃/30h+300℃/10h.After560℃/30h+150℃/10hheat treatment methods, the second phases precipitateswell and uniformly distributed. After homogenization at560℃/30h+300℃/10h, we gotthe lowest hardness of38HV, which is advantageous to the subsequent deformation.After optimized program of homogenization560℃/30h,560℃/30h+150℃/10hand560℃/30h+300℃/10h respectively,TEM is utilized for the microsructuresobservation of Er-added alloys. Iron-rich phase has obvious trend of nodulizing afterthose two-stage homogenization, and a lot of Al-Zr-Er globular phase are detected afterhomogenization of560℃/30h+300℃/10h.Then we did the hot rolling experiments use the Er-added alloy under the threeoptimized programs above. The total deformation is73%. The largest elongation of48%is obtained along the rolling direction after homogenized at560℃for30h.Andafter those optimized two-stage homogenization, fine comprehensive mechanicalproperties (yield strength is80MPa, tensile strength is180MPa and elongation is30%)are obtained.The two-state homogenization can reduce anisotropy of ductility in therolling process, after which comprehensive mechanical properties can be obtained. |
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