Effect Of Mg、Cr And Si On The Crystalline Range And Properties Of 5052 Aluminum Alloy

The 5xxx series aluminum alloys have been widely used due to it has the characteristics of high strength,the good corrosion resistance and the excellent high temperature plasticity and so on.The 5052 aluminum alloy is one of the most widely used products in the 5xxx series,it has the middle-high strength,good fatigue resistance and welding performance,resistance of marine atmospheric corrosion and the excellent low temperature stability,the 5052 board is widely used in aircraft,vehicles,ships,instruments,containers and other products.The 5052 aluminum alloy produced by hot-rolling process,but this technology has the long production flow,the complex process and the cost of production is high.The High-throughput continuous casting and rolling process,by comparison,is a new and efficient aluminum alloy strip blank production technology.It has the advantages of high flow rate,short flow,energy saving and environmental protection,low cost and so on.At present,the mainly problems of the 5052 aluminum alloy that produced by the High-throughput continuous casting and rolling process are the crystallizing range is big and the poor casting fluidity.Those problems will result in segregation,porosity and other defects.These defects are highly “hereditary” and directly influence the performance of finished product board,lead to the performance of finished product plate is not ideal.In this paper,starting from the source of alloy,by changing the composition ingredient of 5052 aluminum alloy,we can reduce the crystallization interval of 5052 aluminum alloy while ensuring the performance of finished products.In order to have the same production conditions as factory basically,this paper design mould and simulation of solidification process of aluminum liquid firstly,to get the same injection moulds as factory’s cooling rate and crystallizing direction.Through the composition design of alloy to get the 5052 aluminum alloy with different content of Mg,Cr and Si of 7 mm thick.Though the methods of microstructre analysis,DSC analysis,energy spectrum analysis,mechanical properties test,corrosion resistance test,researching the effects ofingredients of Mg,Cr and Si on the crystallization range and properties of 5052 aluminum alloy and also explore the rules of recrystallization,provide some theoretical guidance for the mass production of 5052 plates in high throughput continuous casting.The main results are as follows:(1)A casting mold with a wall thickness of 25 mm is designed,and the thickness of the casting plate is 9 mm.Numerical simulation of the solidification process of aluminum liquid,The cooling rate of aluminum liquid is about9.6℃/s(continuous casting and continuous rolling production line 7℃/s~9℃/s)by simulation.Crystallizing direction is from the mold’s side wall to centre.Measured the actual grain size of cast plate is 90μm~98μm(continuous casting and continuous rolling production line 95μm).The guarantee is that the cast plate is basically the same as the production conditions in the factory.(2)When the content of Mg in 5052 aluminum alloy is the same,the addition of Cr of 0.15%~0.35% has no effect on the crystallization interval.The crystallization interval decreases with the reduce of Mg content,the Mg content decreases from 2.8% to 2%,the crystalline interval reduce by 8 degrees,the crystallization interval decreases,the mobility increases,and the segregation degree of alloy decreases.(3)When the content of Cr is the same,the mechanical properties of the alloy increase with the increase of the content of Mg.The Mg content increased0.3%,tensile strength increased 10 MPa.When the content of Mg is the same,the Cr content raised 0.1%,the tensile strength increased 6 MPa.Increasing the equivalent amount of Cr,the strengthening effect of the alloy is better than that of increasing the equivalent amount of Mg.Therefore,It can reduce the content of Mg and increase the amount of trace Cr to ensure the mechanical properties of the alloy..(4)After adding Si elements,the main phase composition of aluminum alloy is Al-Mg phase and Al-Mg-Si phase.The Si content from 0.15% to 0.35%,the crystallizing interval reduced 5℃.The Si is to form Mg2 Si easily with Mg in aluminum alloy,the Si has lost a certain amount of Mg to reduce Mg content,while Mg content is directly related to the crystallization interval,resulting in further reduction of crystallization interval,increased mobility and reduced segregation.(5)When the content of Mg is constant,the tensile strength and yield strength increase with the increase of Si content.The elongation reduced,when Mg content is0.35%,the strength reaches the maximum 208 MPa.(6)After cold rolling,the microstructure is fibrous,and recrystallization occurs at 300 degrees.At 340 degrees,the fiber structure is completely eliminated,and the grain is completely recrystallized.In this process,the hardness of the alloy increases significantly;the cup convex value increases obviously,and the alloy’s deep punching ability is best at 340 degrees.Therefore,the recrystallization annealing process of aluminum alloy can be determined to keep 2h at 340 degree annealing temperature.(7)When aluminum alloy contains 2.2%Mg,0.35%Cr and 0.35%Si,the minimum crystallization interval is 27℃,and the tensile strength is 208 MPa.