Preparation And Relative Basic Research On Al-Mg-Sc Alloy With Middle Strength And Weldability

The Al-Mg-Sc alloy sheets were prepared by semi-continuous casting,hot rollings cold rolling and stabilizing under the condition of industrialization production which dimension was thickness 2mm,by width 1200mm. Using thermal processing simulation and the research of plasticity,hardness measurement and electrical resistance test,tensile test at room temperature and metallographic analysis and electronic microscopy , the mechanical properties,corrosion resistance,microstructure and the variation disciplinarian of microstructure as well as weld properties of Al-Mg-Sc alloy sheets were investigated when the processing technical condition homogenizing and stabilizing treatment technical conditions are different. On the base, the welding properties of Al-Mg-Sc alloy finished sheets were researched. The results show that:(1) The optimum chemical components range of Al-Mg-Mn-Sc-Zr alloy is Al-5.5-6.5Mg-0.15-0.40Mn-0.2-0.4Sc-0.1-0.15Zr-0.02Ti-Be, in which the content of Mg should be controlled above the medium value and the concentration of Mn is limited to the interspace of the range, while that of Sc and Zr can be controlled in 0.25 and 0.12%, respectively.(2) Mn is entered together with aluminum bulks in the form of Al-10%Mn master alloys, being placed upper layer of aluminum bulks. Sc is joined in the form of Al-2%Sc master alloys agent, and Zr is joined in the form of Al-4%Zr master alloys, and both of them are carried when temperature of the melted materiel is over 800℃after aluminum bulks are melted. Ti is joined in the form of Al-4%Ti and Al-5%Ti-l%B master alloys, Al-4%Ti master alloys is joined before analyzing sample, inline in chute the form of Al-5%Ti-l%B master alloys at semi-continuous casting.(3)The best refined processing is made up of the melted refining in furnace and the melted refined online out furnace. During the whole of the latter process, the inert gases with small uniform air bladder are pumped continuously in filter.(4) The angle of mold draining hole for secondary cooling water is redesigned, and the original 45°is changed to 30°. The optimal parameter of melt-cast technical of Al-Mg-Sc alloy is show in the following table: (5) During the homogenization process of the as-cast, there is the precipitation property which is similar with the property of traditional aluminium alloy during the process of aging after solid solution, i.e. oversaturated solid solution formed during the process of semi-continuous sharp quenching casting can be decomposed to precipitate Al₃(Sc,Zr) phase of nanometer size.(6) Besides eliminating the macroscopical stress of the as-cast which decrease the deformation resistance in the process of hot rolling, the main purpose of homogenization is regulating the precipitation property mentioned above, in order to achieve the homogeneous distribution of the particles in the aluminum solid solution matrix.(7) Overall evaluating the property of precipitated particles, decrease of the deformation resistance in the process of hot rolling and the final mechanical property, the best homogenization temperature is 300-350℃, keeping for 8 hours.(8) When Sc-Al-Mg alloy is deformed by compression at high temperature, the natural logarithm of strain rate lnεand flow stress, lnσ, ln[sinh(ασ)] ,ln[sinh(ασ)] and the reciprocal of tempurture 1/T satisfy linear relationship. That's to say, the deformation process of this alloy is similar to a thermal activation process of high-temperature creep process. Thus, the high temperature deformation material constant of this alloy is:we can obtain the equation of flow stress of Al-Mg-Sc alloy deformed by reason of thermal compression as follows :ε= 8.75×10¹²[sinh(0.1336σ)]^5.25exp(-183.201/RT)(9) With the increase of temperature in thermosplastic experiment, the the short time tensile strength of received-alloy is decreased, and the plasticity is increased. The cast at 350℃-400℃has a proper deformation resistance and a good thermal plasticity, so the proper temperature for hot rolling is 400℃-420℃. Under the manufacture conditions, the pass and reduction in pass should be controlled strictly. Reduction in pass and rolling speed should not be oversized at the beginning of rolling. And after the displacement is over 25%, the reduction in pass and rolling speed should be enhanced generally to make sure the deformation distributing in the whole workpiece.(10) The recrystallization temperature of Al-Mg-Sc alloy is higher and may be stabilizing annealinged under higher temperature. The corrosion resistance is worse when the stabilizing annealing temperature is lower then 200℃, and the corrosion resistance of cool-roll plane stabilizing annealinged under the conditions of 200℃/1h is the worst one. Correspondingly, the corrosion resistance becomes better and changes from EB degree to N and P degree, when the stabilizing annealing under the conditions of 300℃/1h. Considering the mechanical properties and the corrosion resistance, the best stabilizing annealing process parameters for the cool-roll planes are 300℃/1h.(11) The matched welding wire is also designed and prepared, which have a very good welding compatibility with the matrix, and the intensity coefficient of the welded joints achieves 86%. The effect of minor Sc and Zr on the joint strength includes two aspect. One is that the minor Sc and Zr refine and strengthen the welded joint structure. The other is the precipitate Al3(Sc,Zr) particles increase the recrystallization softening resistance during the welding thermal-cycle process.(12) The mechanical properties of the as-researched Al-Mg-Sc alloy plane areσb≥415MPa,σ0.2≥302MPa,δ5≥15%, and the exfoliation corrosion property achieves P degree, and the intensity coefficient of the welded joints is more than 0.85. The results meets the requirements roundly.