A Study On Al-Mn-Co Casting Aluminum Alloys Suitable For Anodizing

At present,aluminum alloy complex thin-wall appearance used in 3C products with mobile phone casing as a typical example are mainly made of wrought aluminum alloy through Computerized Numerical Control Machine processing,which is time consuming and inefficient in the utilization of raw materials.The production of aluminum alloy thin-wall appearance by casting aluminum alloy is relatively simple,and the utilization rate of raw materials is also high.However,it is difficult to anodize the traditional casting aluminum alloy with high Si content and the appearance quality is poor after anodization.Therefore,it is necessary to develop a new type of casting aluminum alloy,whose appearance after anodization can meet the requirements of 3C products.In this thesis,Mn and Co were selected as the main alloy elements.Firstly,the microstructure and anodization properties of Al-Mn and Al-Co binary alloys were studied respectively.The influences of Mn and Co content on the macroscopic,microscopic morphology and corrosion resistance of anodic films were investigated.With the increase of Mn and Co content,the thickness,roughness and corrosion resistance of the anodic film of Al-Mn and Al-Co alloy were decreased.The primary Al₆Mn phase in Al-Mn alloy was oxidized to form an oxide layer on the surface after anodization.Al₉Co₂ in Al-Co alloy was dissolved gradually during anodic oxidation.Compared with Al-2.5Mn,the macroscopic morphology of the anodic film of Al-2Mn alloy was less different from those of Al-1Mn and Al-1.5Mn alloy,and the relevant studies of our group incidicated that Al-2Mn possessed good fluidity.Therefore,based on the Al-2Mn alloy,the influences of Co content on the tensile strength,anodic film morphology and corrosion resistance were studied.The results showed that the tensile strength of Al-Mn-Co alloy was increased first and then decreased with the increase of Co content in the range of0%-1.5%,while the tensile strength of the alloy was decreased when the Co content was in the range of 1%-1.5%.In addition,Co resulted in the reduction of the corrosion resistance and the film thickness.Based on Al-2Mn-1Co alloy,0.3%Sc,0.2%Ti and 0.3%Sc+0.2%Ti were added to refine the alloy microstructure and further improve its performance.The addition of 0.3%Sc and0.2%Ti to Al-2Mn-1Co alloy can greatly improve its tensile strength.The tensile strength was increased from 140.8 MPa to 207.1 MPa by 66.3 MPa,with an increase of 47.1%.At the same time,the addition of Sc and Ti can also increase the thickness of the anodic film of Al-2Mn-1Co alloy,reduce the roughness and greatly improve the corrosion resistance.This study developed an aluminum alloy with good anodic oxidation ability that can be used in casting,which has important reference value for the promotion and application of casting aluminum alloy with low silicon or no silicon to produce the appearance of 3C products.The research will also shed light on the development of new aluminum alloys with different compositions from traditional casting aluminum.