Investigation On Hot Rolling Heavy Deformation Mechanism And Corrosion Resistance Of Zu-1.5Cu-0.05Ti Alloy

China is a zinc-rich and copper-less country.To achieve the goal of "zinc substitution for copper" or "saving copper with zinc" in the wider area conforms to our national strategic requirements.Zn-Cu-Ti alloy has a series of advantages,such as self-cleaning,safety,non-toxic,light mass and low cost.As a substitute of copper alloy,Zn-Cu-Ti alloy has been widely used in the field of mechanical electronics,automobile manufacture,roof and exterior wall decoration.At present,there are two problems in the production of Zn-Cu-Ti alloy sheet:(1)The comprehensive mechanical properties of Zn-Cu-Ti alloy sheet need to be improved.In the subsequent processing process,bursting and edge cracking easily occur in the Zn-Cu-Ti alloy sheet produced by the traditional process.In addition,due to its low strength,shapes and sizes of the alloy products are eaily changed in the use,which severely reduces the service life of the product.Therefore,it is imminent to improve the comprehensive mechanical property of Zn-Cu-Ti alloy sheet.(2)China has been ranked as the third most serious acid rain area after European and North American,especially in coastal developed area.The emission increase of industrial pollutants,salt content in the atmosphere resulted in intergranular corrosion,pitting corrosion and stress corrosion of Zn-Cu-Ti alloy.So,it is urgent to study the corrosion resistance of Zn-Cu-Ti alloy.With the optimization process used as a starting point,the forming mechanism of large deformation of Zn-1.5Cu-0.05Ti alloy was investigated,and the influence of deformation(33.3%,50%,60%,66.6%and 71.4%)and deformation temperature(250? and 300?)on the properties of the alloy(such as strength and elongation)were studied as well.It tries to explore the deformation-induced precipitation behavior of ? phase(CuZns)in the hot-rolled Zn-1.5Cu-0.05Ti alloy sheet.revealing the relationship between the deformation conditions and the number,morphology and distribution of ? phase(CuZn5).The relationship between the addition amount of rare earth La and the corrosion property of Zn-1.5Cu-0.05Ti alloy was also analyzed.The results are as follows:(1)Development of the new processing technology.Hot extrusion is used instead of traditional hot rolling cogging process,then large deformation hot rolling is applied.The single pass hot-rolling reduction of Zn-1.5Cu-0.05Ti alloy sheet can be as high as 71.4%.The rolled Zn-1.5Cu-0.05Ti alloy sheet performs excellent hot-rolling properties,having no rolling defects,such as tear,crack and edge crack.In the range of the experiments,the optimal process parameters of Zn-1.5Cu-0.05Ti alloy sheet is as follows:hot extrusion at 300?,hot rolling at 250?,the along with the reduction of 71.4%the tensile strength and elongation of alloy sheet are 264MPa and 53%respectively.Compared with the traditional process sheet,the tensile strength and elongation are increased by 30%?55%,10%?39%.(2)Evolution of morphology and distribution of ? phase(CuZn5)in the hot rolling process.In the alloy sheet,the changes of morphology and distribution of ? phase(CuZn5)can be divided into three stages.In the rolling deformation(from 33.3%to 50%),its morphology of the large lump and uneven band-like aggregation distributes in the matrix.In the rolling deformation(from 60%to 66.6%),The aggregation distribution of ? phase(CuZns)is not only elongated along the rolling direction,but the extent of dispersion distribution increases along the vertical rolling direction.When the deformation reaches 66.6%,? phase(CuZn5)completely disperses in the matrix,and its morphology becomes more tiny granular shape.In the rolling deformation(71.4%),the diffuse distribution of ? phase(CuZn5)decreases,part of ? phase(CuZn5)presenting granular shape and short band-like shape distributes aggregatively in the matrix.(3)Evolution of mechanical properties of Zn-1.5Cu-0.05Ti alloy in the hot rolling process.The elongation of Zn-1.5Cu-0.05Ti alloy has a rising trend with the increase of the hot-rolling deformation.The tensile strength of Zn-1.5Cu-0.05Ti alloy,however,has a falling trend with the increase of the hot-rolling deformation.Under the same rolling deformation,Zn-1.5Cu-0.05Ti alloy has a higher elongation and tensile strength when it is rolled at 250?.(4)Mechanism of the corrosion resistance improvement of Zn-1.5Cu-0.05Ti alloy by the addition of the appropriate amount of rare earth La.The addition of rare earth La can significantly improve the anodic passivation performance of the alloy in 3%NaOH solution.Meanwhile,with increase of La content,the thick skeletal dendrite ? phase(CuZn5),as a cathode,refines and disappears,and the dispersed ?? phase forms,which leads to the decrease in the active cathode area.And thus,the corrosion resistance performance of Zn-1.5Cu-0.05Ti alloy is improved both in 3%NaCl solution and in 3%NaOH solution.After the alloy added with the content of 0.5wt%La is immersed in 3%NaCl solution for 56 hours,the corrosion rate of the alloy is reduced by 56.9%.However,after the alloy added with the same content of La is immersed in 3%NaOH solution for 41 hours,the corrosion rate of the alloy is reduced by 25.32%.