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Fatigue Properties of High Strength Al Alloys under Ultrasonic Fatigue

高强度铝合金超声疲劳下的疲劳性能

基本信息

批准号：
13650096
负责人：
KAWAGOISHI Norio
金额：
$ 0.64万
依托单位：
Kagoshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

The fatigue properties of two high strength Al alloys, Al 6061-T6 and Al 7075-T6, in the life range toward 10^9 cycles were investigated in air and at room temperature under ultrasonic fatigue as well as rotary bending fatigue for the purpose of comparison. Our research shows that(1) Fatigue strength increases in both alloys under ultrasonic fatigue, and the influence of ultrasonic frequency is remarkable in the short life region for Al 7075 and in the long life for Al 6061, respectively, meaning that the characteristic of materials plays an important role in the ultrasonic fatigue study.(2) Fatigue cracks initiate from slip bands and no influence of frequency on the cracking mechanism in the two alloys is recognized. But the crack initiation and its early propagation are suppressed under ultrasonic fatigue. In case of ultrasonic fatigue, crack path changes from the initial nearly vertical direction into approximately 60 degree with respect to the stress axle, and most of fatigue life is spent in the growth of small cracks less than ^-100 micron.(3) Striations are rarely found on the fracture surfaces of ultrasonically fatigued specimens, instead, well developed voids are observed along with brittle cleavages, implying that fracture mode transits from tensile mode to shear mode.Furthermore, ultrasonic fatigue behavior in some high strength alloys such as nickel-base superalloy and marageing steels, is also being investigated in order to better understand the effect of ultrasonic frequency on the strength of metallic materials that have different crystal structures.

研究了Al 6061-T6和Al 7075-T6两种高强度铝合金在空气和室温条件下10^9周次的超声疲劳和旋转弯曲疲劳性能。研究表明：（1）超声疲劳作用下，两种合金的疲劳强度均有所提高，且超声频率对Al 7075和Al 6061的疲劳强度的影响分别在短寿命区和长寿命区显著，说明材料特性在超声疲劳研究中起着重要作用。(2)疲劳裂纹起始于滑移带，频率对两种合金的开裂机制没有影响。而超声疲劳则抑制了裂纹的萌生和早期扩展。在超声疲劳的情况下，裂纹路径从最初的几乎垂直的方向变为相对于应力轴大约60度的方向，并且大部分疲劳寿命花费在小于^-100微米的小裂纹的生长上。(3)超声疲劳试样的断口上很少出现条纹，而是出现沿着分布的孔洞和脆性解理，表明断裂模式由拉伸模式向剪切模式转变。为了更好地理解超声波频率对具有不同晶体结构的金属材料的强度的影响，也在研究中。