铝挤压机培训资料5.docx

1、铝挤压机培训资料5Chapter5 Extrusion of Semifinished Products in Aluminum Alloys5.1 GeneralOf all the materials processed by extrusion, aluminum occupies the predominant role in terms of both production volume and value. Based on the annual volume of production of primary and secondary metal, aluminum is pla

2、ced directly after iron. The majority are alloyed（合金化）to produce wrought（可锻的）alloys and formed into semifinished products of which 25% are extruded. The majority of all extrusion plants, three quarters in Germany, for example, process aluminum alloys, 465,000 t in 1995.The physical metallurgical（治金的

3、）properties of aluminum alloys make them particularly suitable for the extrusion of products very close to the finished shape and with attractive properties. The face-centered cubic (fcc) structure with 12 slip（滑移）systems combined with a high stacking（堆垛） fault energy is a requirement for good cold

4、and hot workability. Corresponding(对应的)to the melting point of 660, the hot-working temperature of aluminum alloys falls in the range of 350 to 550, which can be easily withstood by tools made from suitable hot-working steels. In this temperature range the flow stress is reduced to values that requi

5、re relatively low specific press pressures for processing. The natural oxide(氧化皮)skin gives aluminum an attractive appearance and a good corrosion resistance in the natural state. Increased surface protection is given by anodic(阳极的)oxidation. Aluminum forms age-hardening(时效硬化)alloys with low-alloyin

6、g(低合金)additions that combine good hot workability with a high strength after a simple heat treatment.Sections with an extensive range of function specific cross sections can be extruded within narrow tolerances from aluminum alloys. Hollow sections in the form of rectangular tubes and hollow enginee

7、ring plates offer a high bending and torsional(扭转的)stiffness. The selection of the extrusion process is largely determined by the physical metallurgical properties of the aluminum alloys. The high affinity(类同)to steel and thus the tendency to adhere to all extrusion tools has to be included in the m

8、aterial properties in addition to low extrusion temperature and the good extrusion weldability.Direct hot extrusion without lubrication(润滑)and without a shell is used for the majority of extruded products, including solid and hollow sections from the easily and moderately difficult alloys. Direct ex

9、trusion can be used for practically the entire spectrum(系列)of products, from the simple round bar to complicated sections with a circumscribing circle close to the container cross section. Flat dies are used for solid sections and porthole dies for hollow sections. Indirect extrusion comes into cons

10、ideration for compact cross sections in hard-to-extrude alloys. Cold and hot extrusion with lubrication of the container and the die is also used for bars and tubes.注释:alloyedlid 合金化 wroughr:t 可锻的metallurgical,metl:dikl治金的stacking（stki 堆垛）correspondingkrispndi 对应的oxideksaid 氧化皮anodicndik 阳极的age-hard

11、ening时效硬化 low-alloying低合金torsionaltnl 扭转的affinityfiniti 类同lubrication lubrikein 润滑spectrumspektrm 系列5.2 Extrusion Behavior of Aluminum Alloys5.2.1 Flow StressThe extrusion temperature range, the flow stress variations, and the friction across the tooling determine the extrusion behavior of aluminum

12、alloys. Alloy and quality requirements determine the necessary exit temperature for the extruded product and the temperature range for the deformation. In the range 350 to 550, the flow stress of aluminum alloys is very dependent on the temperature and the composition. The increase in the flow stres

13、s with increasing content of the most common alloying elements is shown in Fig. 5.1 .Figure 5.2 shows for some non-heat-treatable(不可热处理的)alloys that reducing the temperature by approximately 100 results in an almost doubling of the flow stress providing the alloy additions stay in solution(溶液). With

14、 age-hardening alloys similar to Al-MgSi1 the variation of the flow stress is displaced by solution and precipitation(沉淀）processes according to the content of alloying elements in the matrix(基体).注释:non-heat-treatable不可热处理的solutionslu:n 溶液 precipitationprisipitein 沉淀matrixmeitriks 基体Fig. 5.1 Increase

15、 in the flow stress of aluminum in hot working with different alloying additions Fig. 5.2 Flow stress of some non-age-hardening aluminum alloys as a function of the deformation temperature (maximum of the flow curve in torsion tests with 0.655 s-1) 5.2.2 Flow ProcessThe aluminum alloys are almost al

16、ways extruded in direct contact with the container and die manufactured in hot-working steel. However, aluminum exhibits a significant chemical affinity and adhesion tendency with iron. Even in the solid state it tends to adhere to tool surfaces. At face pressures above the flow stress, Coulombs law

17、s of friction lose their validity（正确性) if the shear distortion(扭曲)of the peripheral(外围的)layer requires less force than the slip along the surface of the harder frictional party. The face pressure at the inner face of the container is of the order of 10 times the flow stress. Therefore, aluminum allo

18、ys flow in direct extrusion according to flow type B1 as shown in Fig.5.3.注释:validityvliditi 正确性 distortiondist:n 扭曲peripheralprifrl 外围的5.2.2.1 The Dead Metal ZoneThe billet surface is stationary(静止不动的)relative to the container inner wall, and the shear distortion is at a maximum immediately below t

19、he surface (Fig. 5.4). A dead metal zone forms in front of the face of the flat die. The surface of the extruded section is not formed from the surface of the billet but from the interior of the billet by shearing along the dead metal zone. The outermost layer of the billet surface initially adheres

20、 to the inner wall of the container and is shaved off by the advancing dummy block（挤压垫块）. The material that is compressed together in front of the dummy block and that contains oxide and exudations（渗出物）from the billet surfaces ends up well below the surface of the extrusion following the path shown

21、in Fig. 5.3, No. 2, and forms an incompletely bonded intermediate（中间）layer referred as the piping defect. Material located farther below the surface is compressed at the upper edge of the dead metal zone and follows path 1 of the dead metal zone into the region of the surface of the extruded product

22、. Adhesion of the material also occurs in feeder chambers and in the ports of porthole dies where there is a high pressure.Fig. 5.3 Flow types B, B1, and C and the flow inward of the billet peripheral layer along the dead metal zone (path 1) and from the dummy block edge into the interior of the bil

23、let (path 2) Fig. 5.4 Adhesion of the billet surface to the container wall and the shear deformation of the peripheral layer注释：stationarysteinri 静止不动的 dummy block 挤压垫块 exudation ,eksju:dein 渗出物intermediate intmi:dit 中间5.2.2.2 In the Shape-Producing ApertureThe pressure conditions in the die aperture

24、（孔）are different. The axial pressure at the exit is zero, or there can be a small tensile stress（拉力）if a puller is used. The face pressure, which determines the friction, cannot be easily calculated because it straddles（跨越） two boundary cases. If the section can slide as a solid body through the die

25、 aperture, the face pressure, and thus the friction, is low. If the section undergoes a reduction in thickness through a narrowing die aperture, the face pressure is at least equal to the flow stress. The large adhesion affinity of aluminum increases the friction stress to the same order of magnitud

26、e as the shear stress. The friction in the die opening is responsible for the increase in the axial pressure against the flow direction. Slip with Coulomb friction（库伦摩擦）is impossible in the extrusion of tubes over a mandrel because of the high radial pressure between the billet and the mandrel. If t

27、he extrusion is carried out over a stationary mandrel, relative movement with shear friction takes place between the billet and the mandrel from the start of extrusion over the entire billet length. The relative speed is therefore of the order of magnitude of the stem speed. The billet material is o

28、nly accelerated to the exit speed of the tube as it crosses the deformation zone and at the same time the pressure on the mandrel surface falls rapidly. The transition to slipping friction of the finish extruded tube over the mandrel tip takes place in the region of the die aperture. When a moving m

29、andrel is used, the zone in which relative movement occurs between the billet and the moving mandrel is only the length of the deformation zone. The shear zone moves toward the back of the billet as the extrusion progresses.注释:apertureptju 孔tensile stress 张应力straddle strdl 跨越coulomb friction ku:lm f

30、rikn 库伦摩擦5.2.3 Thermal Balance and Extrusion SpeedIn the direct extrusion of aluminum alloys without lubrication, two to three times the mechanical work is needed than would be required for an ideal loss-free deformation（无亏损变形）. The work carried out by the press on the material being extruded is pra

31、ctically completely transformed into heat, which is partly transferred into the tooling and partly removed in the emerging extrusion. In the adiabatic limiting case（绝热极限情况）, each MPa of average extrusion pressure corresponds to an average increase in temperature of 0.3 K. The magnitude involved is s

32、hown in Fig. 5.5 for the case of an easily extruded material with a flow stress of 25 MPa in which a billet of length L0 = 4D0 is extruded as quickly as possible with an extrusion ratio of 30 to avoid any heat losses. When a material volume corresponding approximately to the volume of the deformation zone is extruded, there is initially a steep increase in temperature. With loss-free deformation, which approximately occurs in the