Microstructures And Properties Of Al-Mg-Sc And Al-Mg-Er Alloy Sheets

Three Al-Mg-Mn alloy plates with0.25%(wt%) Sc,0.10%(wt%) Sc and0.25%(wt%)Er are prepared by casting、hot rolling、cold rolling and stabilizing. These plates have a thickness of2mm. Using research methods of hardness measurement, electrical resistance test、tensile test at room temperature, metallographic analysis and electronic microscopy, the mechanical properties, corrosion resistance, microstructures and the variation disciplines of microstructures and properties are investigated under different stabilizing annealing temperatures. On the base, the TIG welding properties of finished sheets of the three alloys are researched. The results show that:1)0.25%Sc and0.12%Zr adding to Al-Mg-Mn alloy form primary Al3(Sc,Zr), Al3(Er,Zr) intenmatallic particles which can refine as-cast grains greatly. What’s more, the size of as-cast grains of Alloy one is about20μm, while those of Alloy two and Alloy three are about40μ m and70μm,respectively.2) During annealing, three alloys have the same variation rules of microstructures and properties, i.e.with increase of annealing temperature, strength decrease a little but the ductility increase a lot. Under the condition of320℃/1h, the Alloy one has the strongest ultimate strength and yield strength, which are439MPa and339MPa, respectively. Those of Alloy two are414MPa and308MPa. The Alloy three has the weakest ultimate strength and yield strength, which are335MPa and172MPa, respectively.3) Alloy one and Alloy two with Sc can partly keeping processing state fibrous tissue after annealing for1h at300℃,while Alloy three with Er begin to recrystallize under the same condition. This is duo to the fact that Al3(Sc,Zr) can still pin dislocations and subboundaries under300℃, while Al3(Er,Zr) coarse and the ability of restraining recrystallization becomes weaker. 4) The corrosion resistance is worse when the stabilizing annealing temperature is lower than200℃, and the corrosion resistance of cold-rolled plates stabilizing annealed under the conditions of200℃/1h is the worst one which are ED degree for three alloys. Correspondingly, the corrosion resistance becomes better and changes from EB degree to N or P degree when the plates were annealed under the conditions of280℃/1h. Considering the mechanical properties and the corrosion resistance, the best stabilizing annealing process parameter for the cold-rolled plates of the alloys is320℃/1h.5) The ultimate strength, yield strength and the welding coefficient of the three TIG welded joints are as follows:Alloy one:Rm=348MPa,R0.2=240MPa, the welding coefficient is79.6%; Alloy two: Rm=345MPa,R0.2=259MPa, the welding coefficient is80.7%; Alloy three:Rm=289MPa,R0.2=183MPa, the welding coefficient is79.8%. In the HAZ(heat-affected zone) of Alloy one and Alloy two, Al3(Sc,Zr) enables the HAZ still maintains fibrous structures through pining the movement of dislocations and the mergence of subboundaries, so that the HAZ of the two joints still have substructure strengenthing effect, while complete recrystallization happens in a wide range of the HAZ of Alloy three duo to the fact that Al3(Er,Zr) coarse and lose the effect of pining, leading to the disappearence of substructure strengenthing effect.