Optimizing consolidation behavior of Al 7068-TiC nanocomposites using Taguchi statistical analysis

The fabrication of high strength Al 7068？5%TiC （mass fraction） nanocomposite was studied by mechanical alloying and hot pressing routes. Considering densification importance and grain growth effects, hot pressing process conditions for producing bulk nanocomposite were optimized using statistical Taguchi method based on compressive strength achievement. The Taguchi results indicate that 30 min hot pressing under pressure of 500 MPa at 385 °C provides high compressive strength and hardness of 938 MPa and HV 265, respectively. More interestingly, analysis of variance proves that the applied pressure is the most influential factor for hot pressing of the nanocomposite. The contribution percentages of factors in hot pressing terms are as follows： applied pressure （61.3%）, exposed temperature （29.53%） and dwelling hot pressing time （4.49%）.

Microstructure and Quasi-Static Mechanical Behavior of Cryoforged AA2519 Alloy

In this study, AA2519 alloy was initially processed by multi axial forging (MAF) at room and cryogenic temperatures. Subsequently, the microstructure and the mechanical behavior of the processed samples under quasi-static loading were investigated to determine the influence of cryogenic forging on alloys’ subgrains dimensions, grain boundaries interactions, strength, ductility and toughness. In addition, the failure mechanisms at the tensile rupture surfaces were characterized using scanning electron micro-scope (SEM). The results show significant improvements in the strength, ductility and toughness of the alloy as a result of the cryogenic MAF process. The formation of nanoscale crystallite microstructure, heavily deformed grains with high density of grain boundaries and second phase breakage to finer particles were characterized as the main reasons for the increase in the mechanical properties of the cryogenic forged samples. The cryogenic processing of the alloy resulted in the formation of an ultrafine grained material with tensile strength and toughness that are ~41% and ~80% higher respectively after 2 cycles MAF when compared with the materials processed at ambient temperature. The fractography analysis on the tested materials shows a substantial ductility improvement in the cryoforged (CF) samples when compared to the room temperature forged (RTF) samples which is in alignment with their stress-strain profiles. However, extended forging at higher cycles than 2 cycles led only to increase in strength at the expense of ductility for both the CF and RTF samples.

The Effects of Build Parameters and Strain Rate on the Mechanical Properties of FDM 3D-Printed Acrylonitrile Butadiene Styrene

In this paper, the effects of build parameters on the mechanical properties of 3D-printed acrylonitrile butadiene styrene (ABS) produced using fused deposition modeling (FDM) are investigated. Full factorial experimental design incorporating a 2-level, 3-factor design with raster angle, layer thickness and interior fill style was carried out. Tensile tests were performed at four different strain rates to determine how the build parameters influence the mechanical properties of the 3-D printed ABS and to assess its strain rate sensitivity under quasi-static loading. It was found that the modulus of toughness of ABS material is most influenced by raster angle, while the interior fill style is the most dominant build parameter that dictates the specimen’s modulus of resilience, yield strength and ultimate tensile strength. At all strain rates, it is further revealed that higher mean values of yield strength, ultimate tensile strength and modulus of resilience were obtained when the interior fill style is solid as opposed to high density. This can be attributed to the denser structure and higher effective cross-sectional area in solid interior fill style in comparison with high density interior fill style. However, the influence of the layer thickness on the investigated mechanical properties was found to be inconsistent. It was noted that specimens built with both 0.254 mm layer thickness and the cross [0°/90°] raster angle had superior mechanical properties when compared to those built with the 0.3302 mm layer thickness and cross [0°/90°] raster angle. This suggests that there is a key interaction between the layer thickness and the raster angle. At any FDM build parameter, it was found that all the mechanical properties investigated in this work exhibited modest sensitivity to strain rates. This study has provided a platform for an appropriate selection of build parameters combinations and strain rates for additive manufacturing of 3D-printed ABS with improved mechanical properties.

Fatigue Responses of Three AA 2000 Series Aluminum Alloys

In this paper, smooth specimens of three aluminum alloys: AA 2219-T8, AA 2519-T8 and AA 2624-T351, were subjected to the same level of uniaxial (tension/compression) fatigue loading to compare their fatigue responses. Fractographic investigations of the failed specimens after fatigue loading was also conducted using a scanning electron microscope. The fatigue test results showed considerable differences in the fatigue lives of the three investigated alloys with AA 2219-T8 having the shortest fatigue life and AA 2624-T351 the longest fatigue life. The fractographic analysis showed that coalescence of micropores, microvoids, particles cleavage and microcracks are the predominant features in the fracture surface of AA 2219-T8. The fracture surface features of AA 2519-T8 revealed higher resistance to fatigue cracks nucleation and growth when compared to AA 2219-T8. The features depicted mainly partly ductile and partly brittle fracture. The AA 2624-T351 fracture surface features revealed noteworthy ductile failure mechanism. The results suggest a strong correlation between the surface fractographic features and the fatigue lives of the alloys. It is also observed that in addition to the yield strengths and ultimate tensile strengths, the total strain energy densities (SED) may provide a reasonable indication of the relative fatigue performance of the three alloys. AA 2219-T8 had the lowest SED and the lowest fatigue life, while AA 2624-T351 had the highest SED and the highest fatigue life. Thus, AA 2624-T351 would be the most suitable materials for components subjected to fatigue loading.