Texture Evolution and Control of 2524 Aluminum Alloy and Its Effect on Fatigue Crack Propagation Behavior

The influences of cold rolling and subsequent heat treatment on the microstructure evolution of 2524 alloy were investigated using an orientation distribution function (ODF) and electron back-scattered diffraction (EBSD). A preparation method of 2524-T3 aluminum alloy with a strong Brass texture was developed, and its effect on the fatigue properties of the alloy was investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that with the increase in cold rolling deformation from 0% to 80%, the volume fractions of Brass, copper, and S textures in the 2524-T3 alloy also increase, especially in the case of Brass and S textures. However, the volume fractions of cube and Goss textures are reduced significantly, especially for cube textures, which are decreased by 57.4%. Reducing coarse second-phase particles (CSPs) is conducive to the formation of a strong deformation texture during cold rolling. A 10% deformation at each rolling pass, followed by a step annealing, helps the preservation of a Brass texture even after solution treatment at 500 °C for 0.5 h, while a large cold deformation followed by high-temperature annealing helps the formation of a strong cube texture. The Brass texture can enhance the strength while decreasing the fatigue crack growth resistance of this alloy.

Mechanical and Fatigue Properties of Diamond Reinforced Cu and Al Metal Matrix Composites Prepared by Cold Spray

Diamond-reinforced composites prepared by cold spray are emerging materials simultaneously featuring outstanding thermal conductivity and wear resistance. Their mechanical and fatigue properties relevant to perspective engineering applications were investigated using miniature bending specimens. Cold sprayed specimens with two different mass concentrations of diamond 20% and 50% in two metallic matrices (Al – lighter than diamond; Cu – heavier than diamond) were compared with the respective pure metal deposits. These pure metal coatings showed rather limited ductility. The diamond addition slightly improved ductility and fracture toughness of the Cu-based composites; having a small effect also on the fatigue crack growth resistance. In case of the Al composites; the ductility as well as fatigue crack growth resistance and fracture toughness have improved significantly. The static and fatigue failure mechanisms were fractographically analyzed and related to the microstructure of the coatings; observing that particle decohesion is the primary failure mechanism for both static and fatigue fracture.

Fatigue delamination growth characterization of a directly bonded carbon-fiber-reinforced thermoplastic laminates and aluminum alloys with surface nanostructure using DCB test

With the recent demand for weight reduction, structural materials for transportation equipment are being replaced by carbon-fiber-reinforced thermoplastics (CFRTPs). Therefore, techniques to join CFRTPs to alloys are needed. In this study, the fatigue delamination growth of bonded CFRTP/aluminum alloy joints was characterized. The specimens were bonded in three ways, using adhesive, direct chemical bonding, and direct chemical bonding with a nanostructured surface. The type of the specimen was double cantilever beam (DCB) specimen, which consisted of aluminum alloy (A5052) and plain woven CFRTP. The lay-up of the CFRTP was [(0,90)]9 and the used matrix was PA6. Fatigue loading was applied in displacement control mode. The ratio between the minimum and maximum displacement was 0.1, and the test frequency was 5 Hz. The crack length during the fatigue tests was obtained by compliance calibration. Fatigue was characterized by constructing a Paris diagram for each specimen type. The fracture surface distinctively changed from smooth brittle-like fracture to hair-like ductile fracture post fabricating a nanostructure and chemical bonding. As a result, the fatigue crack growth resistance of the specimen with the nanostructure significantly improved due to the hair-like ductile fracture.

Fatigue Crack Growth and Precipitation Characteristics of a High Zn-Containing Al-Zn-Mg-Cu Alloy with Various Typical Aging States

The fatigue crack growth of Al-Zn-Mg-Cu alloy can be adjusted by different aging treatments. In the present work, a high Zn-containing Al-Zn-Mg-Cu alloy was treated by single, double and triple stage aging treatments and typical T6, T79 and T77 states were selected by tensile properties. Fatigue crack growth under these aging states was tested and related fracture morphology and precipitation characteristics were observed. The results showed that fatigue crack growth resistance for the alloy was T6<T79<T77. The corresponding fracture morphology also showed the difference of fatigue striations and the measurement of them provided an additional evidence. The precipitation proved that the alloy with T6 state possessed GPI zone, GPII zone and η' phase while that for T76 state was GPII zone, η' phase and η phase. As for the T77 state, the precipitate types were GPII zone and η' phase. The matrix precipitate for T6 state was smaller and denser than that for T79 and T77 states while that for T77 state possessed a dense distribution than that for T79 state. The measurement of precipitate size distribution also proved it. The grain boundary precipitates for T79 and T77 states were similar, which had a more intermittent distribution than that for T6 state.

Effect of Bond-Line Thickness on Fatigue Crack Growth of Structural Acrylic Adhesive Joints

With an increasing demand for adhesives, the durability of joints has become highly important. The fatigue resistance of adhesives has been investigated mainly for epoxies, but in recent years many other resins have been adopted for structural adhesives. Therefore, understanding the fatigue characteristics of these resins is also important. In this study, the cyclic fatigue behavior of a two-part acrylic-based adhesive used for structural bonding was investigated using a fracture-mechanics approach. Fatigue tests for mode I loading were conducted under displacement control using double cantilever beam specimens with varying bond-line thicknesses. When the fatigue crack growth rate per cycle, da/dN, reached 10−5 mm/cycle, the fatigue toughness reduced to 1/10 of the critical fracture energy. In addition, significant changes in the characteristics of fatigue crack growth were observed varying the bond-line thickness and loading conditions. However, the predominance of the adhesive thickness on the fatigue crack growth resistance was confirmed regardless of the initial loading conditions. The thicker the adhesive bond line, the greater the fatigue toughness.

Near-Threshold Fatigue Crack Growth Behavior of ECAPed Ultrafine-Grained Copper

Fatigue crack growth resistance of ultrafine grained Cu processed by equal channel angular pressing (ECAP) was investigated. Particular emphasis was devoted to the effects of microstructure evolution on fatigue crack growth in the near-threshold regime. The ultrafine grained Cu exhibits a lower fatigue threshold than coarse-grained Cu at stress ratios of 0.1 and 0.7. Fatigue induced coarsening of the UFG structure near the fatigue crack and intergranular fatigue crack growth are observed.