【作者】 袁武华；

【导师】 陈振华； 黄培云；

【作者基本信息】 中南大学 ， 材料学， 2001， 博士

【摘要】 结合“九五”攻关项目和“九七三”项目制备高性能大尺寸耐热铝合金管材的要求，本文对FVS0812耐热铝合金在喷射沉积过程中的规律进行了研究，研制了新的多层喷射沉积制备大尺寸管坯设备。通过对多层喷射沉积制备管坯工艺参数的分析，确定了较佳的工艺参数，并成功地制备出形状和尺寸较好的无裂纹FVS0812合金管坯，管坯尺寸为Φ400×800×115（内径×长×壁厚）。建立了热流分析模型，对管坯热流和显微结构进行了分析。制定了大尺寸高性能管材的挤压工艺和旋压工艺，制备出了性能优良的大尺寸挤压和旋压管材。并对高性能板材的制备工艺进行了探索。其主要的研究结果如下： ⑴对多层喷射沉积制备大尺寸耐热铝合金管坯的原理和FVS0812合金喷射沉积过程中的规律进行了研究和分析。多层喷射沉积制备管坯过程中，雾化器和基体管同时运动，喷射流在沉积面作往复扫描运动，管坯是逐层沉积而成。喷射流在同一位置沉积时的间隔较长，在相对较冷的表面沉积时可以获得约10⁴Ｋ·s^-1以上的冷却速度。而管坯的长度和壁厚分别取决于喷射流的扫描行程和扫描次数。因而具备了制备耐热铝合金大尺寸管坯的可能。耐热铝合金喷射沉积过程中，熔滴的平均粒径和粒度分布均受到雾化气体压力、熔体温度和液流直径等雾化工艺参数的影响。喷射流的空间质量分布呈双峰分布，而喷射流在平面上扫描时，垂直于扫描方向的质量分布近似于高斯分布。随着喷射高度的增加（200～400mm），喷射流的粘结效率和沉积坯致密度降低。而基体材质、表面状况和温度都影响着沉积层的粘结。 ⑵对管坯制备工艺进行了分析，并成功制备了形状和质量较好的无裂纹管坯。结果表明，雾化器平移速度υ_w与基体转速ω_j必须满足关系υ_w≥ω_jr_0.5/π，才能获得表面平整的管坯。而管坯的较优制备工艺可确定为：υ_w=0.1m·s^-1，ω_j=60r·min^-1，雾化气体压力1.0MPa，熔体温度960℃，液流直径4.0mm，喷射高度180～220mm。 （）按照多层喷射沉积制备耐热铝合金管坯的过程，建立了热流分析模 型。根据该模型对不同粒径熔滴飞行过程中的速度、温度、冷却速度、固相甩 分数等以及喷射流沉积后的冷却、凝固及其影响因素进行了分析。结果表明， 雾化过程中，熔滴的直径大，凝固过程中的冷却速度较小，凝固过程在一个 较长的距离内完成。熔滴直径小，则反之。在0＜ 的飞行距离内，0《20卜 粒径的熔嫡均可获得 IXIO‘K·S’以上的平均冷却速度。喷射流沉积后，沉 积层的平均冷却速度可以达到IX10’K＊－’以上。同种工艺条件下，管坯的 长度和直径大，则沉积层冷却速度较高。在轴向中点处，连续两次沉积时冷 却速度相近，而越靠近管坯端部，连续两次沉积时的冷却速度差别越大。通 过雾化粉末和沉积坯的微观结构分析，发现直径较大粉末（22 p m）中有2－5 卜m粗大析出相，晶粒约10－20pm，根据二次枝晶臂间距可估算出其冷却 速度约为 9．5 x二02K·s’。而沉积坯中析相为 20－60run的球形a－Al；。仰，“户，勿 晶粒尺寸200—500run。根据熔滴在沉积面扁平变形现象可以估算出，平均粒 径 90 p m的单个熔滴在基体上沉积时冷却速度为工3 x 10k·s”’。因此，根 据熔滴在0《00mm的雾化飞行阶段和沉积阶段的冷却速度，可推断出管坯 制备过程中熔体凝固时冷却速度应为 IXIOL 10sK·S’之间，高于传统喷射 沉积和雾化制粉工艺。 (4较详细分析了挤压工艺、旋压工艺等对耐热铝合金管材组织结构和 性能的影响，制备了高性能挤压和旋压管材，并对高性能板材加工工艺进 行了探索。研究表明，450℃以上，挤压温度越高，管材力学性能越低。采 用低温长时、高温短时的分级加热制度，在480℃以4．9的挤压系数挤压时， 在现有设备能力下，可获得性能较好的挤压管材。虽然挤压管材的晶粒和 析出相均有长大现象，但无平衡相析出。挤压管材的性能为： 25t，or。。＝310MPa，or。＝391MPa，8＝11．4％；t 350℃，or。。二178MP，rtr二185ma，8三12．SO／O。 其性能明显高于传统喷射沉积挤压态该合金棒材，但与平流铸造挤压 态该合金棒材相比则较低。挤压管材旋压过程中，管材密度随变形程度增 加而提高。旋压温度高于450℃时，将导致管材强度下降。在350℃一420℃ 采用小道次压下量多道次旋压工艺，可以避免管材旋压开裂和性能降低， 并且总压下量较大时，管材性能较高。与挤压管性能相比，总压下量为83o／o 的旋压管材室温屈服强度和断裂强度分别提高 25更多还原

【Abstract】 Combining ~vith a key project supported by the National Ke~?Program of 9 Live year Plan, a novel multi-layer spray deposition ~MLSD) equipment for large dimensions pipe blanks have been developed. Pipe blanks of FVSO812 alloy with dimensions of (I) 400 X 800 X 115mm (inner diameter X length X wall thickness) were J)repared by MLSD technology. Thermal history and microstructure characteristics of the pipe blanks were analyzed. Alloy pipes with high performance were produced by extrusion and spinning process. The main conclusions were drawn as following:(1)The preparation principle of pipe blank with large dimensions by MLSD and the processing regularities were researched and analyzed. In present process, the atomized droplets spraying flow scans reciprocally along the surface of pipe substrate and the blank is deposited layer by layer with the atomizer and substrate moving simultaneously. Thus the scanning range of the spraying flow is large and the internal of the successive deposition at the same point is long ,which leads to a high cooling rate of the deposit above 104K s? So MLSD is more proper for preparation of FVSO8I2 alloy pipe blanks with large dimensions. The mean atomized droplet size and its size distribution were influenced by the atomization process parameters. such as atomization gas pressure (P3, temperature of melt (I) and the diameter of melt flow (D). The spatial matter flow density in the atomization cone presents a bimodal distribution. At the deposition stage, matter density vertical to the scanning direction (MDS) presents an approximate Gauss distribution. The sticking efficiency of the atomized droplets spraying flow and deposit density decrease as the increasing of spray distance (z).(2)Based on an intensive analysis on the process, the needed pipe blanks with fine shape precision and excellent quality were prepared. The results show that, to obtain pipe blanks with flat surface, the atomizer should move evenly and its speed U satisfy such expression as U ~ Lu1 r5/ ~t where Lu is the turning speed of the substrate and r,,5 is the half-width of MDS. The optimum process parameters in present study are as following: U ~0.1m s4, Lu 60r miff? Pz1.OMPa, T=96() ~C, D~4.0mm, z180~-220mm0(3)A one-dimension model of heat flow analysis was established to analysis the cooling and solidification of atomized droplets with different size during the flying and after their deposition. The results show that the average cooling rates of the dropletsxx-ith thc sisc bctuyccn 0 to 220 ll m can reach above 1 X 10’Ii. s-l dufu1g thc fl\-ingdistancc bctween 0 to 2()0min. the cooljng rates of dIop1ets witi1 the mean size of 9()P m can obtain 3.3 X l()’lt. s l after theiI deposihon. The average cooling ratc of thcdeposited la\-er can reach above 10’K. s-’. So it can be concluded that the couljng rateduring MLSD is about 103tw 105K. s-’, which is higher than that either in convenh<)l1alspra\’ deposihon and or in atoforahon. The dricrostructures of the atomizcd poxt.derparticles xt’ith different size xt7ere tested. The results shou- that the grains about 1() to 2()P m and needle-shaped phase with the size between 2 to 5 ll m are prescnted in thcpowder particles above 220 ll m. But in the deposiL the grain slze is ouly between 20()to 500nm wlth sphetical parhcles Q -Al,,(Fe,V),Si about 20 to 60nm.(4) The influences of densdriahon process on the rhastructures and propertiesof the allo}-’s piPes have been investigated. Extruded and spun p1Pes xv~id1 fineperfOrmance have been produced. The results show that the boe dixnensions extrudedpipe wtth high performance can be rnanufactuxed within the capacaq of the availableextiuding apparatus wtth optimUm processing. The mechanical properhes ofas-extruded piPes are apparend3 higher than that of extruded bar b}’ com,enhonalspra}’ deposition. The mechandal properhes of the extruded piPes are llstcd asfUll<)\L,ing.25’C f o ..==3l0MPa, o,=391MPa, 6 =11.4’/O;350OC, O .,==178MPa, o,=185MPa, 6 =12.5?,o.When更多还原