The Mechanical Properties And Fluidity Improvement Of Al-Cu And Al-Mg Alloys By AlTiC-B Crystal Seed Alloy

Al-Cu alloy is a kind of high-strength aluminum alloys with high mechanical properties at both room and high temperatures;Al-Mg alloys have low density,high strength,good plastic toughness,excellent cutting workability and corrosion resistance,especially the capability to resist electrochemical corrosion.But the poor performance in casting hinders the application of these two alloys.As solid-solution alloys,microstructures of Al-Cu and Al-Mg alloys are usually dominated by coarse dendrites because of wide crystallization temperature range during solidification.Coarse dendrites reduce fluidity of the alloys and increase the tendency to generate hot cracks,which deteriorate the casting performance of the alloys.Fluidity is the most important property for casting of alloys,which has an important influence on the formability and mechanical performances of castings or ingots.Grain refinement technology can not only enhance the strength and plasticity of aluminum alloys,but also improve the fluidity and reduce the casting defects Grain refinement by adding grain refiners is the most ideal method due to its stable effect,high efficiency and low cost.In this paper,the refining behavior of B-doped AlTiC-B crystal seed alloy on Al-Cu and Al-Mg alloys have been studied.Further,the influence of grain sizes and morphologies on the mechanical properties and casting properties of the alloys was analyzed.And the mechanism was revealed as well.The main results of this article are as follows:(1)Effect of the AI-5Ti-0.2C-0.3B crystal seed alloy on microstructure of the cast ZL205A alloy was studied.It showed that the average grain size of the ZL205A alloy was reduced from 766 ?m to 61 ?m when 0.5%crystal seed alloy was added,and after holding for 60 min,it was still 103 ?m.Average length of the fluidity sample was increased from 554 mm to 678 mm,with an increase of 22.4%;Ultimate tensile strength of the alloy was 552 MPa,which increased by about 12.4%,and yield strength was increased to 472 MPa,which was increased by about 8.3%;Elongation was 8.3%,which was about 56.6%higher than the unrefined alloy.(2)Influence of the Al-5Ti-0.2C-0.3B crystal seed alloy on grain morphology of 2024 alloy was studied,and fluidity of 2024 alloy was tested by a single spiral fluidity sample method.It was found that with the increase of addition level of the Al-5Ti-0.2C-0.3B crystal seed alloy,the grain size decreases and the fluidity and mechanical properties increases.When the addition amount of the crystal seed alloy was 0.3%,average length of the fluidity sample was increased from 867 mm to 1216 mm,with an increase of about 39.1%;The Brinell hardness of the 2024 alloy was 127.6 HBW,which was about 15.6%higher than that before refined;The ultimate tensile strength increased by about 15.2%to 387 MPa and the elongation was 2.53%,increased by 73.3%.(3)Grain size of the ZL303 alloy was decreased with the increase of addition level of the Al-5Ti-0.2C-0,3B crystal seed alloy,but the refining effect tends to be gentle.When adding 0.5%Al-5Ti-0.2C-0.3B seed alloy,it achieved the best refinement effect with grain size of the alloy reduced to 115 ?m.Through grain refinement,length of the fluidity sample for the alloy was increased from 1285 mm to 1397 mm,which was increased by about 8.7%.This enhanced the feeding capability of liquid metal and reduced the tendency to generated hot cracks.With the increase of the added amount of crystal seed alloy,the ultimate tensile strength of ZL303 alloy has been significantly improved.When the adding amount was 0.5%,the ultimate tensile strength of the alloy was 229 MPa and the elongation was 5%,which respectively improved by about 5.1%and 117%compared to the alloy before refinement.