航空材料学报

2013, 33(2): .

[Abstract](1328) [PDF 278KB](283)

Abstract:

Effect of Additions with Trace Sc and Er on As-Cast Structure of Al-Cu-Mg-Zr Alloys

LI Yun-tao, LIU Zhi-yi

2013, 33(2): 1-7.

[Abstract](1647) [PDF 2582KB](376)

Abstract:
Three experimental Al-Cu-Mg-Zr alloys added with trace Sc and Er were prepared by ingot metallurgy (IM) method.The effect of additions with trace Sc and Er on the as-casting structure of the Al-Cu-Mg-Zr alloys was studied by using optical microscope,scanning electron microscope (SEM) and X-ray diffraction (XRD).The results show that the grain refinement of addition Sc to the alloy is attributed to the dispersive particle Al3 (ScxZr1-x) formed from the melt during the solidification proceeding. These particles refine as-casting grains remarkably and are the ideal nucleus of Al growth. Er is assembled in the grain boundary in the form of Al8Cu4Er. During solidification, Er is segregated at the front of liquid-solid phases interface and increases the composition undercooling of the alloys. It restrains the dendritic growth and refines the corresponding as-casting grain.

Effects of Hot Rolling Deformation on Microstructure and Mechanical Properties of TiBw/Ti6Al4V Composites with Network Microstructure

HUANG Lu-jun, TANG Ao, RONG Xu-dong, GENG Lin

2013, 33(2): 8-12.

[Abstract](1858) [PDF 1730KB](304)

Abstract:
Based on the successful design and fabrication of network structured TiBw/Ti64 composites with a superior combination of mechanical properties, effects of hot rolling deformation on the microstructure and mechanical properties of TiBw/Ti64 composites with a network microstructure were investigated in the present study. The SEM microstructure results show that the microstructure of the deformed composites depends on the rolling reduction. In the TiBw/Ti64 composites with a network microstructure, the broken TiB whiskers gradually increase and the local volume fraction of TiBw reinforcement on the network boundary decreases with increasing the rolling reduction. The Ti64 matrix exhibits a transformed microstructure. The tensile test results show that the ultimate tensile strength and elongation of the novel TiBw/Ti64 composites firstly increase and then decrease with increasing the rolling reduction. This phenomenon is attributed to the combined actions between the deformation and heat treatment strengthening effects of matrix and the weakening effect breaking the TiB whiskers. The ultimate tensile strength of the network structured TiBw/Ti64 composites is increased from 1090MPa to 1330MPa, that is to say, it is increased by 22%. Moreover, the elongation is increased by 97%.

Microstructure Characteristics and Mechanical Properties on Consolidation of Pure Al Particles through Equal Channel Angular Pressing and Torsion

WANG Xiao-xi, LI Ping, XUE Ke-min, WANG Xue, ZHANG Xiang

2013, 33(2): 13-18.

[Abstract](1667) [PDF 2850KB](311)

Abstract:
Equal channel angular pressing and torsion (ECAPT) were used as a technique for consolidating pure Al particles at 200℃. The influence of ECAPT passes number on pure Al compacts was analyzed in terms of microstructure, density and mechanical properties using electron backscattering diffraction (EBSD), transmission electron microscopy (TEM), microhardness test and density measurement. It was found that microstructures after 1 pass were featured elongated grains of intensively sheared powder particles with low angle boundaries. The materials were further refined along with the increased microhardness and density by increasing the number of ECAPT passes. At the same time, dynamic recovery and dynamic recrystallization were occurred during ECAPT processing. After 4 passes of ECAPT, full density was achieved. The microstructure was consisted of ultrafine grains of 0.5m in size and equiaxed in shape with mostly high angle boundaries. The grain refinement mechanism was related to intensive shearing, strain accumulation as well as dynamic recrystallization. The improvement in the mechanical properties of the compaction was attributed to microstructure densification and grain refinement.

Effect of Stress on Microstructure and Mechanical Properties during Age Forming Process of 7050 Aluminum Alloy

LI Chao, DAI Sheng-long, ZHANG Kun, RU Ji-gang

2013, 33(2): 19-23.

[Abstract](1763) [PDF 1164KB](366)

Abstract:
Under the normal ageing and stress ageing condition, the effects of external stress on the ageing precipitation behavior of pre-aged 7050 aluminum alloy were studied by micro-hardness and transmission electron microscopy (TEM). The results show that the external stress during ageing accelerates the age-hardening process of pre-aged 7050 aluminum alloy, and decreases the hardness of peak ageing and shortens the time of under aged stage. The external stress enhances the precipitation behavior and increases the precipitation growth. The TEM observation shows that the property changes of the alloy during stress ageing process are closely related to the evolution of microstructure. In the early stage of stress ageing process, the precipitation of ' makes the increase of hardness to peak value. Then, the transition of 'to and the coarsening of lead to the decrease of hardness.

Microstructure and Mechanical Properties of Friction Stir Welded Al-Li Alloy Lap Joints

ZHANG Dan-dan, QU Wen-qing, ZHUANG Lai-jie, YANG Mo-cong, CHEN Jie, MENG Qiang, CHAI Peng

2013, 33(2): 24-28.

[Abstract](1709) [PDF 2394KB](358)

Abstract:
Two different Al-Li plates with 2mm thickness were successfully joined via friction-stir welding method, and the microstructure and mechanical properties of overlap joints were analyzed. The effect of welding parameters and artificial aging on the overlap joints were investigated. The results showed that the typical onion ring feature occurring in the weld nugget zone consisted of refined and equiaxed grains. The hooking defects appear at the interface of overlap joints in the advancing side, which compromise significantly the load bearing capacity of joints. The elongation of joints was only 3.18%, less than 25% that of base metal. When the rotation speed was 800r/min and welding speed was 200mm/min, the ultimate strength of joints reached 467MPa, that as much as 94% of the base metal. After artificial aging, the peak tensile strength was increased to 526MPa, and there were the obvious growth in measured ultimate strength and the corresponding reduction in the elongation of joints. In addition, the tensile fracture surface analyses indicated that the tensile cracks initiated from the hooking defects and the fracture mode of overlap joints was quasi-cleavage and dimple composite fracture.

Influence of Oxygen/Fuel In-Gun Ratio on Structure and Properties of CoCrAlYTa Coating Prepared by Detonation Gun Spraying

GAO Jun-guo, LU Feng, TANG Zhi-hui, WANG Chang-liang, GUO Meng-qiu, CUI Yong-jing

2013, 33(2): 29-34.

[Abstract](1669) [PDF 1771KB](337)

Abstract:
Detonation gun spraying method was employed to prepare CoCrAlYTa coating. The influence of oxygen/fuel in-gun ratio on structure and properties of CoCrAlYTa coating was investigated by means of SEM, EDS, micro-hardness tester and adhesive strength measuring, etc. The results reveal that the detonation combustion temperature and shock wave energy increase with the increase of oxygen/fuel in-gun ratio, which induces the transformation of the coating structure from uniform structure to lamellar structure and the decrease of the coating porosity. It was also found that the micro-hardness, adhesive and bending strength of the coating were increased with the increase of oxygen/fuel in-gun ratio.

Synthesis of Intermetallic Compound Al₂CuMg

ZHOU He-rong, CHEN Ming-ming, DU Cui-wei, MA Jian, JIE Gan-xin, LI Xiao-gang

2013, 33(2): 35-40.

[Abstract](1636) [PDF 2349KB](329)

Abstract:
Al2CuMg material was manufactured by vacuum smelt and heat treatment according to different component materials of Al-Cu-Mg alloy phase diagram. The component, phase, microstructures are investigated by scanning electron microscope, energy spectrum analysis and X ray diffraction. The results show that the bulky Al2CuMg phase is gained by vacuum smelt, directional solidification and water-cooling of component materials of the proportion as 51Al-33Cu-16Mg. But the content of other phases is more. The proportion of Al2CuMg phase material which is obtained by vacuum smelt, solidification, water-cooling and 72 hours heat treatment of component material as 50Al-25Cu-25Mg is above 98%.

Wear and Friction Characteristics of Ti6Al4V Alloy

MAO Yi-shu, CUI Xiang-hong, WANG Shu-qi, LI Dong-sheng, YANG Zi-run, SUN Yu

2013, 33(2): 41-45.

[Abstract](1724) [PDF 2520KB](299)

Abstract:
The wear and friction characteristics of Ti6Al4V alloy were studied. The results show that the wear rate at 25℃ gradually increases with the increase of load. At 200℃, the wear rate under low loads is slightly higher than that at 25℃, and the wear rate starts to increase rapidly above the load of 200N. At 400℃, wear rate decreases under the load of 50-100N, slightly increases under the load of 100-200N, and rapidly increases above 200N. The main wear mechanisms at 25℃ and 200℃ are adhesive wear and abrasive wear respectively. At 400℃,oxidative mild wear is prevailed under the load of 100-200N. It is found that mechanic mixing layer is formed on worn surfaces. When the load of 100-200N is applied at 400℃, tribo-oxides appear on worn surfaces. In this case, the hard mechanic mixing layer possesses an obvious wear-reduced role.

Local Fatigue Behavior of 7075 Alloy under Condition of Rotational Fretting Wear

SHEN Ming-xue, ZHOU Yan, SONG Chuan, MO Ji-liang, CAI Zhen-bing, ZHU Min-hao

2013, 33(2): 46-50.

[Abstract](1885) [PDF 1478KB](298)

Abstract:
Rotational fretting wear tests of 7075 aluminum alloy against 52100 steel ball under the different angular displacement amplitudes were carried out on a new rotational fretting wear testing rig. The initiation and propagation behavior of local fatigue cracks induced by rotational fretting wear were studied based on the micro-analysis of surface and profile morphologies of wear scars. The results show that the fatigue cracks distribute mainly in the mixed fretting regime (MFR) under the condition of rotational fretting wear, and most of them propagate into the matrix alloy. In the MFR, the material failure mechanism mainly was as a result of fatigue crack initiation and propagation accompanied with particles detachment by delamination. In the partial slip regime (PSR), the fatigue crack expanded parallel to the direction of the surface and the fretting damages were mainly slight delamination. In the slip regime (SR), the fatigue effect weakened and the wear of material was dominant during the competition process between the local contact fatigue and wear. In additional, the formation of local fatigue crack was closely related to the central convexity under the rotational fretting wear.

Preparation and Electromagnetic Properties of Zn²⁺ Substituted W-type Ba-Co Ferrites

WANG Xiao-ya, HUANG Ying, ZHAO Yang, WU Yan-fei

2013, 33(2): 51-57.

[Abstract](1679) [PDF 2579KB](290)

Abstract:
The Zn2+ substituted W-type Ba-Co ferrites powder, BaZnxCo2-xFe16O27(x=0.8, 1.0,1.2) was prepared by a sol-gel method. The powder was characterized by X-ray diffraction, scanning electron microscope, vibrating sample magnetometer and vector network analyzer. The influence of sintering temperature and Zn2+ content on the crystal structure was studied。The particle appearance, magnetic properties and electromagnetic parameters of the sample with different Zn2+ content were analyzed. The results show that the average grain size was about 25.06-32.04nm, the particle size was about 3-9m,well-distributed and regular shaped W-type Ba-Co ferrites powder with hexagonal flake structure was obtained by sol-gel method at 1300 ℃. The maximum Ms reached to 105.99 Am2kg-1 when x=1.2. And the magnetic loss increased with the rising Zn2+　concentration in the range of 4-11GHz, the value was 0.2-0.8, while it decreased with the rising Zn2+　concentration in the range of 11-18GHz, the value was 0-0.5.

Hygrothermal Properties of Ramie Fiber/Phenolic Resin Composite under Different Hygrothermal Conditions

CHEN Xu, YIN Peng, XIAN Gui-jun, LIU Yan-feng, LIU Qing-man, YI Xiao-su

2013, 33(2): 58-65.

[Abstract](1616) [PDF 1670KB](331)

Abstract:
Ramie fiber fabric reinforced phenolic resin composite laminates were prepared, and the moisture absorption, diffusion properties and mechanical properties were studied under different hygrothermal conditions. Results show that instantaneous moisture absorption rate of the laminate increases with the increase of relative humidity at 20℃,40℃ and 60℃, and that the temperature has unobvious effect on the hygrothermal properties of the laminate under 50% relative humidity. When the moisture absorption fraction is less than 0.5, the moisture diffusion coefficient of the laminate are 2.1610-6 cm2/s, 2.9410-6 cm2/s and 6.6110-6 cm2/s respectively under the temperatures of 20℃,40℃ and 60℃, and the relative humidity of 50%. The mechanical properties of the laminates decrease with the increase of the moisture absorption rate. The SEM photographs indicate that the moisture absorption damages the interface adhesion between fiber and resin of the composite, resulting in weak stress transferring between the fiber and the resin matrix.

Distribution of Wall Thickness and Damage of Rectangular Tube with Different Fillet in Bending Process

ZHOU Shu-hui, LIU Yu-li, SHEN Hua-wen, YANG He

2013, 33(2): 66-73.

[Abstract](1670) [PDF 3791KB](329)

Abstract:
In order to research the damage and wall thickness distribution of 3A21 thin-wall rectangular tube with different fillet in the bending process, the material parameters of Lemaitre criterion were obtained through cyclic loading-unloading tensile tests by using the method of Young's modulus weakening. A user-defined VUMAT subroutine combined Lemaitre criterion was developed based on ABAQUS/Explicit platform. Furthermore, 3D finite element models for bending process of rectangular tube with different fillet were built and the reliability was validated. The results show that the maximum wall-thinning and damage value locates at the section of 50?, and the wall-thinning and damage value increases with the fillet radius decreases. In other words, the tube is more prone to rupture with the cross-section of tube tending to be rectangular.

Fatigue Properties of TC21 Ti-Alloy under Uniaxial and Multiaxial Cyclic Variable Amplitude Loading

TIAN Yu-jie, SHANG De-guang, CHEN Hong, LIU Jian-zhong

2013, 33(2): 74-80.

[Abstract](1664) [PDF 3106KB](329)

Abstract:
The fatigue properties of TC21 Ti-alloy for thin-wall tube specimen are investigated under uniaxial, tension-torsion proportional, non-proportional and variable amplitude loading. All tests are strain-controlled. The results indicate that cyclic softening behavior is shown for TC21 alloy under uniaxial and proportional tension-torsion constant amplitude loading, and the cyclic softening is more obvious under large strain amplitude loading. The large strain loading followed by small strain loading under non-proportional loading, shows that the cyclic hardening for tension stress is responded in the smaller strain loading stage due to the previous larger strain loading strengthening for tensional properties.

Initial Fatigue Quality of Faster Holes of TC4 Titanium Alloy with Two Microstructures

LI Hua, HE Fei, MA Ying-jie, LEI Jia-feng, JING Lyu-lu, LIU Yu-yin

2013, 33(2): 81-86.

[Abstract](1526) [PDF 1921KB](305)

Abstract:
Fatigue crack growth a-N data of TC4 titanium alloy with bimodal and lamellar microstructure was obtained from fracture surface by marker load technique. Based on three different stress levels, the general distribution of equivalent initial flaw size (EIFS) was established to describe the initial fatigue quality (IFQ) of the two microstructures. The results show that, compared with lamellar structure, the IFQ of TC4 titanium alloy with bimodal structure is a high level titanium alloy, in which the IFQ is affected by both the initiating cycles of fatigue crack and the crack propagating coefficient. The fracture morphology in bimodal microstructure by marker load technique was analyzed. It was revealed that the model of fatigue crack propagation changed after the marker load added, which lead to the readable marker line in fracture surface.

Progress and Key Problems in Research and Fabrication of Fiber Reinforced Metal Matrix Composite

WANG Tao, ZHAO Yu-xin, FU Shu-hong, ZHANG Yong, ZENG Wei-hu, WEI Jia-hu, LI Zhao

2013, 33(2): 87-96.

[Abstract](1795) [PDF 1385KB](492)

Abstract:
Types and aerospace applications of the fiber reinforced metal matrix composites were introduced firstly, and then the key problems in research and application of fiber reinforced metal matrix composites were analyzed. Based on the above discussion, the research methods and cores of the key problems were put forward. The interface between fiber and metal matrix is one of the main problems, and the weakness of interface is researched from the surface modification of fibers, interfacial wettability and compatibility, interfacial reaction and strength, and so on. The research of damage mechanisms of composites should be enhanced, and the estimate system of damage will be instituted to instruct the applications. In addition, advanced forming processes and welding technologies are the important issues to decrease the cost and improve the quality of the composites.

2013 Vol. 33, No. 2