Influence Mechanism Of Crystal Orientation On Corrosion Behavior Of Aluminum Single Crystal Under Different Conditions

Aluminum and aluminum alloys are widely used as structural materials in automobile,ship and aerospace because of their high density and high specific strength.The results showed that the crystal orientation has a great influence on the corrosion resistance of aluminum and aluminum alloys,but the mechanism of the effect of crystal orientation on the corrosion behavior of aluminum and aluminum alloys is not clear.Taking aluminum single crystal as the research object,from the perspective of crystal orientation,this paper studies the influence mechanism of crystal orientation on the corrosion behavior of aluminum single crystal under corrosion and stress corrosion,and obtains the following conclusions:(1)The crystal orientation has a great influence on the electrochemical properties of pure aluminum single crystal.The corrosion current density(Icorr)of polarization curves of pure aluminum single crystal samples with four orientations of Cube,Brass,S and R are 0.426μA/cm2 、 0.699 μA/cm2 、 0.91 μA/cm2 and 0.757 μA/cm2 respectively.The corrosion resistance of the samples with four orientations from high to low is: Cube > Brass > R > S.(2)In 3.5% NaCl solution and EXCO solution,with the extension of corrosion time,the corrosion resistance of Cube,Brass,S and R orientation samples first decreased and then increased.After 7 and 15 days of corrosion,the self corrosion potential(Ecorr)of aluminum single crystals with different orientations is Cube > Brass > R > S from high to low.After 15 days of corrosion in EXCO solution,the Ecorr of S-oriented sample is the lowest,reaching-0.793 V(vs.SCE).After stress corrosion in 3.5% NaCl solution and EXCO solution,the corrosion resistance of four kinds of oriented aluminum single crystals is Brass > Cube > R >S from high to low.In the same corrosion solution,with the increase of stress,the Ecorr of four kinds of oriented aluminum single crystals gradually decreases,while Icorr gradually increases,indicating that the corrosion resistance of the sample gradually decreases.(3)In 3.5% NaCl solution and EXCO solution,the corrosion depth of four kinds of oriented aluminum single crystals increased continuously with the increase of corrosion time,and the corrosion depth of S-oriented aluminum single crystal was the deepest.After 30 days of corrosion in 3.5% NaCl solution,the deepest corrosion depth of S-oriented sample is 68.5μm.After 30 days of corrosion in EXCO solution,the corrosion depth of S-oriented samples reached 267.1 μm.The corrosion depth is 11.5% greater than that of Cube-oriented samples.The tensile strengths of Cube,Brass,S and R oriented aluminum single crystals are 40.1 MPa,49.3 MPa,28.5 MPa and 39.9 MPa respectively.Under the stress of 12.0 MPa,the corrosion life of Cube,Brass,S and R oriented aluminum single crystals in 3.5% NaCl solution is 189 hours,205 hours,155 hours and 168 hours respectively.(4)After 7 days of corrosion in 3.5% NaCl solution and EXCO solution,the main corrosion products of four kinds of oriented aluminum single crystals are Al2O3,A(OH)3 and Al Cl3,in which the content of Al Cl3 is relatively small,and the content in 3.5% NaCl and EXCO solution is 2.9% and 27.3% respectively.The thickness of oxide film on different crystal surfaces is different,and the thickness of oxide film on(002)crystal surface reaches21.0 nm.The thickness of oxide film on(010)crystal surface is 5.9 nm,only 28.1% of(002)crystal surface,so(002)crystal surface is the most difficult to be corroded.