After adding Cu to aluminum,the strength of the alloy is improved,and the Cu element in the compound reduces the electrode potential of aluminum,and also reduces the corrosion resistance.For example,adding Mg to the Al-Cu alloy of the slit sheet,non-connection point etching,and mask plate constitutes an Al-Cu-Mg alloy(such as LY11,LY12,etc.),also known as Dura aluminum alloy.Adding Mn to the Al-Cu alloy constitutes an Al-Cu-Mn alloy(such as LY16,LY17,etc.).There are also a series of Al-Cu alloys such as Al-Cu-Mg-Fe-Ni,AI-Cu-Li,Al-Cu-Mg-Si and A1-Zn-Mg-Cu.
In each series of Al-Cu alloys,there are different intermetallic compounds.Al-Cu-Mg alloys mainly include CuAI2,CuMgA1:and so on.Al-Cu-Mn alloys mainly include CuA12,CuMn2 Al:and so on.Al-Cu-Li alloys mainly include CuA12,LiCuAI12,Lie Cub A11:etc.AI-Cu-Mg-Fe-Ni alloys mainly include CuMgA12,FeNiAI,etc.Al-Mg-Si-Cu alloys mainly include CuA12,Mgt Si,CU4 Mg5 S14 Al and so on.In the A1-Zn-Mg-Cu alloys,there are mainly MgZn2,Mg3 Zn3 Al:and so on.
Among these phases,except M$2 Si,MgZn2,Mg3 Zn3 Al:etc.which belong to the anode phase,the rest are cathode phases.
Al-Cu alloys all have common corrosion behavior.This series of multi-component aluminum alloys have pitting corrosion,intergranular corrosion,stress corrosion and exfoliation tendencies,especially the intergranular corrosion sensitivity of shrapnel connectors.The intergranular corrosion of this series of alloys is almost unavoidable.When the intergranular precipitates are distributed in fine and continuous chains,forming a corrosion channel,the intergranular corrosion tendency of the alloy is more serious.The texture etching of this series of alloys is often dominated by intergranular corrosion,and the uniformity of pitting corrosion is difficult to control,especially when the acid-base two-step method is used for higher roughness etching.
LY12 is the most commonly used alloy in this series(Alcoa 2024).The alloy hard-state grade(LY12-Y)has surface roughness up to Ra=1.5 or more after single alkaline texture etching,and has both brightness and uniformity.The surface effect of another natural aging grade(LY12-CZ)after a single alkaline texture etching treatment is equivalent to that of Al-Mn alloy.
