Influence Of Al On The Microstructure And Magnetostriction Strain Of Fe₈₁Ga₁₉ Alloys

Fe-Ga alloys have the advantages of smaller magnetic drive, higher Curie temperature, Better mechanical properties, low cost and Simple preparation process. But their magnetostrictive strain are very low, which limit their application.However, addition of the third element effect on Fe-Ga alloys magnetostrictive strain is one of the research hotspot in Fe-Ga alloys.This paper studied the effect on Fe-Ga alloys magnetostrictive strain by adding Al element with different concentration and different heat treatment process. The as-cast Fe81Ga19-x Alx(x=0.2,0.5,3,6,9) alloys were prepared by nonconsumable arc furnace.The alloys was annealed insulation for 8 hours at 1000 degrees and filled with argon gas.And then cool the Fe81Ga19-x Alx to the room temperature. Preparation of Fe81Ga19-x Alx thin ribbon by melt-spun. And the thin ribbon was annealed insulation 10 min at 1000 degrees and filled with argon gas. The magnetostrictive properties and microstructure were studied by optical metallography, X-ray diffraction(XRD), Vibrating sample magnetometer and magnetostrictive measurement. The following results showed that:The microstructure of as-cast and annealed Fe81Ga19-x Alx alloys were made of A2 phase. The alloys by addiing Al element have coarse grain and more points on corrosion.When the cast Fe81Ga19-x Alx alloy melting, the defects occurred, the black spots appeared after corrosion. The saturation magnetostrictive strain of as-cast Fe81Ga18.8Al0.2 alloys was the largest, close to 120×10-6. And the largest magnetostrictive strain of the annealed Fe81Ga19-x Alx alloys is Fe81Ga18.5Al0.5 alloys, close to 117×10-6. The magnetostrictive strain curves of as-cast Fe81Ga19-x Alx alloys were more smooth after annealing.There are obviously A2 and Modified-DO3 phases of melt-spun Fe81Ga19-x Alx alloys for the figure of XRD. Exists in the Fe81Ga19-x Alx alloys thin ribbon in some amorphous structure. Those amorphous structure is disappear after annealing. Fe81Ga18.8Al0.2melt-spun ribbons had the largest magnetostrictive strain of 343×10-6. And the Fe81Ga16Al3 of annealing ribbon had the giant magnetostrictive strain of 1056×10-6.According to the analysis of magnetostrictivestrain curve, it has not reached the maximum value. Fe81Ga19-x Alx alloys by melt-spun and after annealing magnetostriction strain have become large. Melt-spinning Fe81Ga19-x Alx alloys magnetostrictive strain increased because of the Modified-D03 phase generated in the process of rapid quenching and the Magnetic crystal orientation of Modified-D03 special phase structurechanged. Melt-spinning and annealing Fe81Ga19-x Alx alloys shift from amorphous to Modified-D03 to A2 phase in XRD figure, the mechanism of the increase of magnetostrictive strain reacted obviously on the phase structure.