| In this study, three kinds of materials, 2024 Sc, 2024 Sc matrix composites with 2wt.%2mm and 3mm length short carbon fiber were fabricated by liquid stirring casting method.The microstructure, fractograph were observed by means of optical microscope technology（OPM） and scanning electron microscope technology（SEM） The EDS energy spectrum analysis technology was used to analyze the phase in materials. The density and compactness of materials were measured using Archimedes principle and immersion test and compared with the theoretical density and compactness. The mechanical properties and micro-yield strength of materials treated with various aging process were measured with tensile test and loading- unloading test. The dimension stability of materials were evaluated by measuring the change of the notch size of 2mm thick ring with a 26 mm out diameter and 24.5mm inner diameter..The results shows that:（1） The microstructure of both 2024 Sc aluminum and 2mm and 3mm carbon fiber reinforced 2024 Sc composites were composed with dark grey α-Al base phase and white primary phase around α-Al that containing Cu, Mg elements and a small amount of elements such as Sc, Zr, Mn, O, which may be Al2 Cu Mg, Al2 Cu, Al3（Sc, Zr） etc. The extrusion of materials resulted in the grains were elongated along the extrusion direction and the white primary phase distributed discontinuously along the elongated grain. The carbon fiber in materials tend to be parallel to the extrusion direction from the random distribution in as-cast materials.（2） The as-cast 2024 Sc aluminum alloy and 2mm and 3mm short carbon fiber reinforced2024 Sc aluminum matrix composite had high porosity and oil absorption rate. The density and compactness were significantly increased after extrude. The porosity of as-extrued materials was reduced by 57.2%, 50.6% and 57.2% respectively for as-extruded 2024 Sc aluminum alloy and 2mm and 3mm short carbon fiber reinforced 2024 Sc aluminum matrix composite. The addition of the carbon fiber, the density, porosity and oil absorption rate increased,while density decreased. Compared with 3mm Cf reinforced 2024 Sc aluminum matrix composites, 2mm Cf reinforced 2024 Sc aluminum matrix composites with higherporosity and oil absorption rate and lower density.（3） The heat treatment（solution at 500 ℃ /4h,and then aged at 130 ℃ /3h+ 200 ℃ /（5h,10 h,15h）） made the yield strength, tensile strength and elastic modulus 2024 Sc aluminum alloy and Cf reinforced 2024 Sc aluminum matrix composites increased firstly and then decreased while the elongation firstly decreased then increased with the aging time.Compared with 2024 Sc alloy, the addition of carbon fiber in the carbon fiber reinforced composited resulted in the yield strength, tensile strength, and elongation of composite material decreased while the elastic modulus increased. However, the fractur and pulling out of carbon fiber resulted in the materials prematurely fractureed. Compared to the 2mm short carbon fiber reinforced 2024 Sc aluminum alloy, 3mm short carbon fiber reinforced 2024 Sc composites had higher strength and modulu.The optimum yield strength, tensile strength and elastic modulus reached to 315MPa、465MPa、82.3GPa respectively,which was increased by5.9%,1.8%,3.3%.compared with 2mm short carbon fiber reinforced 2024 Sc composites.（4） The micro-yield strength of 2024 Sc aluminum alloy and 2mm/3mm short carbon fiber reinforced 2024 Sc aluminum alloy composite firstly increased then decreased with aging time. The materials treated with peak aging process had the highest micro-yield strength,which reached to 294.5MPa、256MPa and 276 MPa respectively for 2024 Sc aluminum alloy and 2mm/3mm short carbon fiber reinforced 2024 Sc aluminum alloy composites. The strain-hardening rate of the materials at micro-yield stage was firstly increased then decreased also, and showed greater strain hardening rate than the initial macroscopic yield stage. The addition of carbon fiber caused more defects in materials and resulted in the decrease in the micro-yield strength. Compared to 2mm hort carbon fiber reinforced composites, the micor-yield strength of the 3mm short carbon fiber reinforced 2024 Sc composite increased by7.8%.（5） After heat treatment that solution at 500℃/4h,and then aged at 130℃/3h+ 200℃/10 h,the 2024 Sc alloy has the maximum instantaneous notch size of aluminum ring after electric park cutting. The addition of carbon fiber caused the obvious decrease in the instantaneous notch size of ring. The 2mm short carbon fiber reinforced 2024 Sc compositeshowed the smallest instantaneous notch size. It shows that the addition of carbon fiber obvious improves the dimensional stability of materials. With the prolongation of hold time in room temperature, all the notch size of three kinds of materials increased slightly firstly then tended to stable, which is related to the high stress and its release in composites.It shows that it is true that the addition of the carbon fiber is favor to the improvement in dimensional stability of 2024 Sc alloys. |
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