7085铝合金的淬透性

通过端淬试验和大尺寸锻件合金淬火试验研究了3种成分7085铝合金的淬透性。端淬试验表明:成分Al-7.0Zn-1.41Mg-1.50Cu-0.14Zr,Al-7.48Zn-1.51Mg-1.42Cu-0.15Zr及Al-7.95Zn-1.80Mg-1.59Cu-0.15Zr 3种合金的淬透深度均大于150mm,而7075合金(成分:Al-5.62 Zn-2.51 Mg-1.60 Cu)仅有38.5 mm,大尺寸合金淬火试验证明了7085合金高的淬透性。通过比较3种7085铝合金T76时效后的硬度和电导率,及与大、小淬火试样比较,淬火后,相对较大的试样比小试样硬度高、电导率低,主要是由于较大试样淬火应力高,导致晶格畸变大造成。研究结果证明,7085铝合金具有极佳的淬透性能,同时建议提高Zn/Mg不应低于4.4。     

A357合金淬火敏感性的研究

为了揭示铸件性能对热处理过程淬火冷却条件的敏感性，研究了淬火介质及淬水转移时间对A357合金析出相与力学性能的影响。结果表明，热处理T6态合金的强度和硬度随着淬火冷却速率的增加而增大，而相对延伸率呈减小的趋势。强度和硬度随淬水转移时间的延长而减小，而相对延伸率先增大后减小。差示扫描量热仪(Differential Scanning Calorimetry，DSC)实验表明，不同淬火冷却条件下析出β’-Mg2Si亚稳相的量和Si相的形态是合金力学性能变化的主要原因。     

热处理状态对限制模压-轧制2A97铝锂合金板材晶粒细化的影响

研究了热处理状态对2A97铝锂合金板材限制模压-轧制工艺晶粒细化和力学性能的影响.将2A97铝锂合金板材分别进行"固溶淬火(AQ)"及"固溶淬火+过时效(OA)"预处理,随后均进行限制模压-轧制试验.采用光学显微镜及电子背散射衍射进行金相观测,对板料进行硬度测试以评估其力学性能.结果表明,AQ态及OA态材料经过限制模压...     

冷却速度对TC2钛合金板材β淬火组织的影响

通过水淬+空冷复合的方式,实现了在一个试样上淬火的冷却速度从水淬到空冷的不同,进而研究了冷却速度对TC2钛合金板材β淬火组织的影响。结果表明,β淬火时冷却速度不同,使得淬火后合金的金相组织存在较大的差别,进而对成品板材的组织产生影响。TC2合金板在热轧过程中获得了球状-纤维状的混合显微组织,水淬+空冷复合试样的水淬部分均发生马氏体转变,但转变的进程有所不同,水淬+空冷复合试样的空冷部分均为片状组织,随着冷却速度的降低,α片丛明显长大,α片宽度变大。淬火的延迟会导致板材显微组织不均匀。     

淬火工艺对7075合金力学性能的影响

利用电子万能试验机和扫描电镜研究了淬火工艺对7075合金力学性能的影响,确定了合理的淬火工艺参数。结果表明,淬火处理温度范围虽然较宽,但7075合金在490℃时即有过烧的危险,综合考虑,淬火温度应选择(470±5)℃;淬火水温应控制在40℃以下;淬火转移时间应控制在30s以内;淬火至时效处理的时间间隔对板材力学性能影响不大。     

时效处理对7050铝合金厚板材料组织、性能及残余应力的影响

采用末端淬火实验、剥落腐蚀实验、透射电镜(TEM)和X射线残余应力测量仪等方法研究不同时效处理制度对7050铝合金厚板材料组织、性能及残余应力的影响。结果表明:T74时效状态试样较T6时效状态试样沿整个冷却方向上力学性能更加均匀;T74时效状态试样的剥落腐蚀性能较T6有显著提高,且淬火冷却速度对T74状态影响不大;沿整个淬火冷却方向上T74时效状态试样残余应力水平较T6时效状态试样明显降低。     

轧制及热处理对医用Mg-2Zn-0.5Nd-0.5Zr合金板材力学性能和耐蚀性能的影响

用挤压轧制方法制备了厚度为1 mm的Mg-2Zn-0.5Nd-0.5Zr合金板材,并对板材进行后续退火和时效热处理,利用光学显微镜、扫描电镜、拉伸、电化学以及浸泡试验等研究了不同轧制温度和热处理对板材力学性能和耐蚀性能的影响.结果 表明:轧制温度从280℃升高到330℃,合金中的Nd元素析出量减少,第二相形貌改变,板材塑性和耐蚀性提高,伸长率由9.1％提高到15.2％,腐蚀速率由0.48 mm/y降低到0.28 mm/y.退火后板材伸长率和耐蚀性均进一步提高,其中330℃+T2处理的合金板材的综合性能最好,其抗拉强度和屈服强度分别为235 MPa和158 MPa,伸长率为24.3％,腐蚀速率为0.12 mm/y.时效处理后,合金的晶界处有大量的析出相析出,第二相强化效果显著,330℃+T6组的抗拉强度和屈服强度最高,分别为275.8 MPa和255.5 MPa,但板材伸长率仅为7.6％,腐蚀速率升高到0.43 mm/y.     

热疲劳环境下多元Al-7.5Si-4Cu合金的裂纹萌生扩展

研究了多元Al-7.5Si-4Cu合金在不同热处理状态下的热疲劳性能。结果表明,与铸态试样和淬火+时效热处理试样相比,T6态试样的力学性能最好,微观组织均匀,热疲劳性能最优良。当热循环次数≥10 000时,T6状态与淬火+时效试样由于Si相和A12Cu相的出现降低了裂纹扩展速率,铸态试样由于A12Cu相复熔球的存在导致裂纹扩展速率急剧上升。     

S390粉末高速钢真空气淬的显微组织及性能

研究了不同淬火温度、不同冷却方式对S390粉末高速钢进行真空热处理的显微组织及性能的影响。试验结果表明,经不同工艺淬火后,S390粉末高速钢的晶粒度在13级左右,其中的合金碳化物数量减少、尺寸变小,硬度均大于63.2 HRC。经真空气淬后的S390粉末高速钢试样中均可得到下贝氏体组织,且在下贝氏体片状组织中及残留合金碳化物周围有纳米椭圆(球)状合金碳化物析出。     

内浇包熔体温度对7075/6009复合板材组织性能的影响

采用双流浇注连续铸造方法,通过改变内浇包熔体温度制备了7075/6009合金铸锭.重点研究了不同内浇包熔体温度下所制备的7075/6009铸锭经过自由压制和轧制变形后的组织和性能.结果表明:7075/6009合金板材在轧制和热处理状态下,当内浇包熔体浇注温度从680℃升高到780℃时,其抗拉强度、屈服强度都会提高,而伸长率变化较小,这主要是由于内浇包熔体温度升高,导致外层合金厚度减小,内层合金在复合材料中的体积分数增加.合金板材在T6热处理状态下获得的最优力学性能是:抗拉强度为404 MPa,屈服强度为364 MPa,伸长率为15.3%.     

'Quench sensitivity' of 7075 aluminium alloy plates

Abstract

7075 aluminium alloy is widely used especially in those applications for which high mechanical performances are required. In the technical literature it is well known that the corrosion resistance and the mechanical properties of this material strongly depend on the cooling rate during quenching. This phenomenon is known as 'quench sensitivity'. The main aim of this paper is to investigate the influence of the cooling rate during quenching of samples taken from plates by varying the parameters of the heat treatment and the rolling direction (L, LT and ST). All the samples were heat treated in laboratory equipment to reach T6, T76 and T73 tempers. The samples were prisms (13 × 13 × 100 mm) and were quenched in water; the cooling rate was imposed by changing the water temperature or changing the polymer amount in a water agitated bath at 20°C. In each of the experimented condition, the cooling rate was measured by a thermocouple placed in the sample. Moreover, a finite element method (FEM) simulation was carried out in order to estimate the heat transfer coefficient during the cooling in all the experimented conditions. Tensile and intergranular corrosion tests were performed to point out the influence of the investigated cooling rates.     

Effects of cooling rate and annealing treatment on sensitization of austenitic-ferritic duplex stainless steel

Duplex stainless steel has higher corrosion resistance and better mechanical properties than conventional type 300 series stainless steel. The corrosion behavior of duplex stainless steel is strongly dependent on the ratio, shape, size and distribution of austenite and ferrite phase in the microstructure. The relationship between the microstructure and the corrosion behavior of the duplex stainless steel was studied. For this purpose, the duplex stainless steel samples were solution heal treated at 1150°C followed by either cooling at various rates (water quenching, air coooling, furnace colling with door opened and door closed) to 820°C and then water quenching to room temperature, or quenching to room temperature and annealing heat treatment at 840°C for various lengths of time. A double loop electrochemical polentiodynamic reactivation (EPR) test was carried out to examine the effect of various cooling procedures or annealing treatment on the sensitization of duplex stainless steel. The grain size, shape, and distribution of the two phases were examined under microscope. From the test results, the relationships were discussed among heat treatment, electrochemical properties and microstructure.     

Effect of thermomechanical history on intergranular corrosion of extruded AlMgSi(Cu) model alloy

The effect of cooling rate after extrusion, solution heat treatment, mechanical deformation and aging on intergranular corrosion (IGC) of two model AlMgSi alloys with different Cu content was investigated using an accelerated corrosion test. The low Cu extrusions (0.02 wt%) were resistant to IGC while the high Cu (0.17 wt%) variants were susceptible in certain tempers. Slow cooling in air introduced IGC. The IGC susceptibility was reduced and finally removed by artificial aging. Water quenching prevented IGC, but severe IGC was introduced by slight aging (underaging). Peak aging (T6) generally reduced IGC susceptibility regardless of cooling media. Overaging further reduced IGC, usually at the expense of introducing pitting. IGC susceptibility was related to the microgalvanic coupling between enriched Cu on the grain boundaries (noble) and the adjacent solute depleted zone (active). Cu enrichment was caused either by slow cooling in air or slight aging of water quenched samples. High IGC resistance was obtained either by keeping the Cu content low or by applying proper heat treatment to high Cu samples. For the present high Cu samples, artificial aging to peak strength provided at the same time the necessary IGC resistance.     

Current research in Egypt on optimisation of combined mechanical strength and corrosion behaviour of steel rebar

Abstract

The effect of accelerated water cooling on the mechanical and corrosion properties of steel rebars produced from steel with composition of 0·17–0·286%C, 0·62–0·72%Mn, 0·15–0·20%Si has been assessed. The bars were rolled from continuously cast steel billets to 12, 16, 20 and 25 mm diameter. Immediately after the last rolling stand the steel bars entered the quenching box. Cooling conditions were varied by changing the number of cooling nozzles and the water flowrate. Initial bar temperature and equalised temperature were calculated using a mathematical model and recorded by pyrometers at the entry of the quenching box and the entry of the cooling bed. Corrosion resistance was determined potentiodynamically and by immersion tests in NaCl and Ca(OH)₂ solution. Equalising temperature decreased with increasing cooling time and water flowrate. Yield strength and ultimate tensile strength (UTS) increased and elongation decreased with decreasing equalising temperature, indicating that different steel grades can be obtained from billet of the same composition using accelerated cooling. Though no direct relationship was observed between mechanical properties and corrosion resistance, the results indicate that cooling conditions and process parameters for thermomechanical treatment should be selected on the basis of corrosion requirements as well as to produce the desired mechanical properties.     

铸锻复合成形AZ91D摩托车发动机壳体热处理工艺研究

采用不同固溶和时效热处理工艺对液态铸锻双控成形AZ91D摩托车发动机壳体进行了热处理实验。结果表明：样品经过T4（415℃x9h,60℃水淬）处理后,合金的抗拉强度和延伸率最大,其值分别为239．7MPa,1．58％,较未热处理提高幅度分别为41．6％,79．9％。经T6（415℃×9h,60℃水淬＋205℃×16h,空冷）处理后,样品显微组织中的第二相得到均化,在一定程度上强化了合金。未处理态、T4、T6状态下的拉伸试样断口形貌中均存在较多的韧窝,表明铸锻双控成形制件的塑性较好。T6（415℃×9h,60℃水淬）热处理后的拉伸试样断口形貌中韧窝最多,塑性最好。     

基于H13钢水淬在线监测的热处理数值模拟优化

为准确预测厚度较厚的H13钢热处理过程中的温度场和淬火残余应力,对规格为φ300 mm×350mm的H13钢工件进行淬火实时温度监测,分别设置了位于芯部、亚表面(离外表面10 mm)、1/3R(离圆心50 mm)和2/3R(离圆心100 mm)处的监测点。考虑钢/水对流换热系数受沸腾条件和热辐射的影响,对对流换热系数h进行了优化。结果表明各个温度监测点的试验结果与计算结果相符,证明经过优化后的对流换热系数可应用于大截面尺寸工件温度场的预测。模拟工件淬火后的应力场并结合显微组织观察发现,淬火在750 s前后出现芯部、表面最大的拉压峰值应力差,证明大尺寸工件淬火存在淬火危险期。     

Effect of microstructure on the mechanical and corrosion behaviors of a hot-extruded nickel aluminum bronze

In this paper,the influence of microstructure on the corrosion behavior of a hotextruded nickel aluminum bronze was studied.Three kinds of samples subjected to the hot-extrusion,annealing and quenching conditions were prepared and immersion tests in 3.5% NaCl solution were carried out.Microstructures and corrosion surface morphologies of the samples were observed by SEM.It was found that the retained β martensite and(α+κⅢ) lamella eutectoid in the as hot-extruded material were eliminated after annealing,and...     

H型钢腹板冷却波浪的调整

针对H800mm×300mm×14mm×26mm及H700mm×300mm×13mm×24mm等宽腹板窄翼缘大规格H型钢存在的腹板冷却浪问题,通过减少腹板冷却水、控制腹板和翼缘尺寸、减缓腹板在冷床上的冷却速率,腹板冷却浪得到较好控制。     

Study on inhomogeneous cooling behavior of extruded profile with unequal and large thicknesses during quenching using thermo-mechanical coupling model

The interfacial heat transfer coefficient between hot profile surface and cooling water was determined by using inverse heat conduction model combined with end quenching experiment. Then, a Deform-3D thermo-mechanical coupling model for simulating the on-line water quenching of extruded profile with unequal and large thicknesses was developed. The temperature field, residual stress field and distortion of profile during quenching were investigated systematically. The results show that heat transfer coefficient increases as water flow rate increases. The peak heat transfer coefficient with higher water flow rates appears at lower interface temperatures. The temperature distribution across the cross-section of profile during quenching is severe nonuniform and the maximum temperature difference is 300 °C at quenching time of 3.49 s. The temperature difference through the thickness of different parts of profile first increases sharply to a maximum value, and then gradually decreases. The temperature gradient increases obviously with the increase of thickness of parts. After quenching, there exist large residual stresses on the inner side of joints of profile and the two ends of part with thickness of 10 mm. The profile presents a twisting-type distortion across the cross-section under non-uniform cooling and the maximum twisting angle during quenching is 2.78°.     

Mg含量和冷速对Mg-Cu-Zn-Y非晶复合材料微观结构及腐蚀行为的影响

采用水冷铜模法和水淬法制备得到Mg65+x(Cu0.66Y0.34)30-xZn5(x=5,10,15)非晶及其复合材料。并通过XRD、SEM对材料结构进行表征,研究Mg含量和冷却速度对样品微观结构的影响。结果表明:由水冷铜模法得到的x=5样品为单一非晶,x=10和15样品是由非晶相与Mg固溶体相组成的非晶复合材料。而利用冷速较低的水淬法得到的样品为非晶复合材料,其主要由Mg,Mg2Cu,MgZnY和非晶相组成。通过研究合金在NaCl中性溶液中的腐蚀行为,发现随着Mg含量的增加,样品的耐腐蚀性能有所下降。并且对于同成分的合金,由冷速较快的水冷铜模法得到的样品耐蚀性相对较好。