Technical Studies On Purification And Modification Treatment Of Recycled Al-Si Alloy Melt

Aluminum scraps'recycling is an inexorable trend of the development of China aluminum industry,because it can relieve the issues of resource shortage and environment pollution.Furthermore,its effect of energy conservation and emission reduction is obvious.This study mainly targets the purification of recycled aluminum melt.Firstly,the inclusion removal theory of the refining flux is studied more systematically,and then a high-efficient,eco-friendly and low-cost refining flux is developed based on the inclusion removal theory.Meanwhile,in order to overcome the process defect of KR stirring purifying technology to the greatest extent,process parameters of KR method are optimized by CFD numerical simulation.In addition,inquiry experiments about modification and refinement of Fe-rich recycled aluminum-silicon alloys are conducted.The main results are as followed:?1?The thermodynamic and wetting analysis of spreading,separating,and refining properties of the flux have been made.The results show that the interfacial tension is a crucial physical parameter for flux.Although the lower?_Flux-Melt is helpful for flux to spread over the melt surface and to remove inclusions,excessive low?_Flux-Meltlux-Melt makes it difficult for flux to be separated from Al melt.Moreover,the lower?_{Flux-Inclusion}lux-Inclusion and the higher?_{Melt-Inclusion}elt-Inclusion are also good for flux to wet solid inclusions.When KF,AlF₃,K₃AlF₆ and KAlF₄ are added into equi-mass NaCl-KCl molten salt respectively,AlF₃,K₃AlF₆ and KAlF₄ can reduce?_Flux-Melt slightly,and reduce?_{Flux-Inclusion}lux-Inclusion to varying degrees,and KF can significantly reduce?_Flux-Melt and increase?_{Flux-Inclusion}.According to testing results of coalescence behavior,it is clear that the removing ability of oxide film for KF,K₃AlF₆ and KAlF₄ is stronger,while the removing ability of oxide film for AlF₃ is weaker,furthermore,the removing ability of oxide film for K₃AlF₆ and KAlF₄is almost same,but both of them is inferior to KF.?2?A novel multifunctional refining flux has been developed.The novel flux has excellent purification and separation properties with the optimum added quality of flux?0.15 wt%?and fluxing temperature?740°C?.After the purification for the ADC12 melt,the hydrogen content decreases to 0.09 ml/100gAl,the oxygen content decreases to 3 ppm,the maximum size of inclusion decreases to 9.8?m,the K value decreases to 0,the average volume fraction of voids and inclusions decreases to 0.031%,and the sample's pinhole degree is equal to level one.What is more,dry dross is generated,the aluminum content in dross is only 8.2 wt%.It is also found that the sodium content in Al melt before and after fluxing treatment doesn't show obvious change.?3?The KR stirring purifying technology has been simulated.Compared to the traditional Star impeller,the newly-designed XSR impeller has the characteristic of pumping,and smaller area of the dead region and higher turbulent kinetic energy are obtained within the melt simultaneously.The mixing effect under the eccentric stirring is superior to the case of centric stirring.For the XSR impeller,in the range of the discussed process parameters,the optimal immersion depth and rotational velocity are 315 mm and 550 rpm,respectively.The experimental data are in well accordance with the simulated results.?4?The modification and refinement of Fe-rich secondary Al-Si alloys have been discussed.With the addition of Y into Al-7Si-0.3Mg alloy containing 1.0 wt%Fe,?-Fe phases and??Al?grains are refined remarkably,meanwhile,eutectic phases are modified.With addition of 0.3wt%Y,the average length of?-Fe phase decreases to²0?m and the finest?-Fe phases are obtained,in the meantime,the eutectic silicon particles are present in fully modified form,and the secondary dendrite arm spacing?SDAS?reaches the lowest value?¹6?m?.The corresponding Y-modified alloys in T6 heat treated condition obtain the best tensile properties compared with other experimental alloys,with the corresponding ultimate tensile strength?UTS?and elongation?EL?values being 384 MPa and 4.9%,respectively.Furthermore,the tensile properties of 0.3 wt%Y modified alloys exceed the properties standard for Al-7Si-0.3Mg alloy,approximately 30.17%for UTS value and 63.33%for EL value.