| As one of the most commonly used lightweight materials,aluminum alloy has excellent properties such as low density,high specific strength,and good plasticity,making it widely used in the fields of automobiles,electronics,aviation,and construction.With the rapid development of the automotive electronics industry in recent years,the market has put forward higher requirements for the performance of aluminum alloy materials.In addition to requiring aluminum alloy materials to have higher mechanical properties,corrosion performance is also an important performance that cannot be ignored.Poor corrosion performance will greatly limit the application range of the alloy.Therefore,studying the corrosion resistance of aluminum alloys has very important practical significance and theoretical value.This paper uses microstructure characterization to study the microstructure characteristics of ADC 12 aluminum alloy after different treatments.Through electrochemical measurement and immersion corrosion experiments,the corrosion performance of a series of ADC 12 aluminum alloys is studied,in order to obtain aluminum alloys with better corrosion performance in the future.Provides strong theoretical support.The addition of rare earth reduces the distance between the secondary dendrite arms of the ADC 12 alloy,the Si phase is transformed from a rough long needle shape to a fibrous shape,the ?-Al phase is refined into an ellipsoid shape,and the rough bulk?-Al5FeSi phase is also refined to small blocks in a certain extent.The addition of 0.9 wt.%Yb,due to the low solid solubility of rare earth Yb,makes Yb gather at the front of the solid-liquid interface during the solidification of the alloy,thereby hindering the melting and diffusion of the solute,resulting in supercooling of the alloy components Increase,therefore refine the composition phase of the alloy,so that the microstructure of the alloy is improved.The Si phase and ?-Al5FeSi phase of ADC12 alloy after hot extrusion are extruded and refined into small blocks or short rods along the extrusion direction.And the addition of rare earth Yb makes the Al3Yb intermetallic compound formed in the alloy.The results of immersion corrosion test and electrochemical experiment show that the corrosion current density(8.56 ?A·cm-2)of the alloy added with 0.9 wt.%Yb and hot extruded is higher than that of the untreated as-cast alloy(17.33 ?A·cm-2)is 50.6%lower.And the polarization resistance(9252 ?·cm2)is 71.3%higher than that of the untreated as-cast alloy(2654 ?·cm2).Due to the addition of Yb and the hot extrusion treatment,the cathode phase in the corrosion micro-cell is refined to varying degrees,resulting in a decrease in the area ratio of the cathode and anode phase,thereby reducing the cathode reaction rate in the corrosion micro-cell,resulting in the corrosion rate of the alloy reduce.After solution treatment at 520? for 5h,the microstructure of ADC 12 alloy changed greatly.The Si phase is basically rounded after solution treatment,most of which are short rods,and a few are granular;the Si phase of the rare earth aluminum alloy after solution treatment is basically fine granular,and due to the lower solid solution of Cu element Temperature,after solution treatment,the soluble Al2Cu phase is basically dissolved into the matrix.The weight loss hydrogen evolution test shows that adding 0.9 wt.%Yb and performing solution treatment can make the alloy have the best corrosion resistance.Similarly,the Tafel polarization curve and EIS test results show that the corrosion current density of the ADC12+0.9 wt.%Yb+ST(4.87 ?A·cm-2)sample is lower than that of the as-cast alloy(18.51 ?A·cm-2),and the impedance value of the former(1852.97 ?·cm2)is much higher than the latter(389.71 ?·cm2).The solid solution of the Al2Cu phase reduces the number of corrosion micro-batteries formed during the corrosion of the alloy,thereby improving the corrosion resistance of the alloy.The optical microstructures of different aging treatment alloys show that the Si phase and ?-Al5FeSi phase of the alloy after T6,DA and RRA treatments have been refined to different degrees.The refining effect of rare earth aluminum alloy after RRA treatment is the most obvious.In addition,the corrosion resistance of the alloy shows that the alloy exhibits severe pitting corrosion after T6 treatment,and the corrosion type of the alloy after DA and RRA treatment changes to intergranular corrosion,but after RRA treatment,it only shows local lighter intergranular corrosion.corrosion.The electrochemical test and the average corrosion rate of weight loss show that the corrosion rate of the alloys with different aging treatments in descending order is:T6>DA>RRA>0.9 wt.%Yb+RRA.Compared with T6 treatment,the precipitated phase of the alloy is reduced after DA treatment,and the degree of element enrichment is relatively low.After RRA treatment,the size of the precipitated phase in the alloy is reduced.In addition,the rare earth aluminum alloy after RRA treatment is due to the modification of rare earth,the organization has been further improved.The distribution,quantity,and size of the secondary phases in the alloy change due to the deepening of the aging degree,which reduces the corrosion potential difference between these phases and the matrix,thereby improving the corrosion resistance of the alloy. |
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