Effect Of Rare-earth Modification On Microstructure And Mechanical Properties Of Al-Fe Based Alloys

Al-Fe intermetallic compound has excellent heat resistance, wear resistance and oxidation resistance, but for the Al-Fe based alloys, because the morphology of Al-Fe intermetallic compound is coarse needle or flake and it splits matrix and affects the mechanical properties of alloys. So this paper mainly studied the effect of rare-earth modification on the microstructure and mechanical properties of Al-Fe based alloys. Firstly, by adding different amount of Ce-rich mixed rare-earth(RE) we have modified Al-Fe based alloys to refine the grains and to improve the harmful morphology of iron-rich phases. Secondly, the Al-Fe based alloys were annealed at different temperatures. Finally, the annealed Al-Fe based alloys were rolled at room temperature with different deformation ratio to further refine the microstructure and improve the morphology of iron-rich phases so as to effectively improve the mechanical properties of Al-Fe based alloys. The optical microscope, XRD, SEM and EDS were used to analyze the metallographic microstructure, phase composition, element content and distribution.For the Al-1wt%Fe alloy, it was shown that when the RE addition is 0.3wt%, the modification effect produced the furthest primary grains and the flake and needle-like Al-Fe phases were changed into the short rods or elliptic ball; By homogeniouly annealing at 480℃for 24 h the acicular and rod-like Al-Fe phases in the grain boundaries were decomposed; Further by the rolling deformation at room temperature the Al-Fe phases were broken into fine particles. With the deformation degree increasing, the Al-Fe phases were distributed in the matrix more uniformly. It proved that without rare earth the tensile strength of the alloy is 84.03 MPa, when adding 0.3wt% rare earth, it is 86.42MPa; while after 80% rolling deformation it has the hightist value which is 163.2MPa with 0.3wt% rare earth. The elongation of the alloy is 24% without rare earth; however it is 27.6% when the addition of the rare earth is 0.3wt%; after 80% rolling deformation the value is 7.46%.For the 8011 A alloy, the best modification effect was yielded when adding 0.3wt% RE. Moreover, the other alloying elements further changed the Al-Fe phases from the flake, rod and needle into the short rod and needle or even granular shapes; Annealing at 450℃ for 24 h made the Al-Fe phases decomposed; the rolling deformation at room temperature further reduced the grain size and broke the Al-Fe phases and made them distribute uniformly in the matrix. It is shown the tensile strength of the alloy is 116.32 MPa without rare earth, when it adds 0.3wt% rare earth, it is 117.46MPa; by 80% rolling deformation it has the hightist value which is 202.65 MPa with 0.3wt% rare earth. When the ally has none rare earth, the elongation is 25%, however it is 28% when adding 0.3wt% rare earth; by 80% rolling deformation the value is 6.83%.For the high-content of Al-Fe alloys, it was observed that the morphology of the Al-Fe phases changed from long rod into coarse needle or coarse flake with an increase of the iron content. When the Fe content was 6.0 wt%, the Al-Fe phases were changed into the coarse needle or coarse snowflake; when the RE amount increased to 0.7wt% and 0.9wt%, the modification effect was the best, the flower-flake, coarse-plate and needle-likes iron-rich phases were changed into the thin needle, thin plate, short rod and elliptic ball. After the annealing treatment, long needles of the Al-Fe phase were decomposed into short rod or particular shape. This means that the annealing treatment has a spheroidizing effect.