Fatigue Characteristic Analysis of New ECO7175v1 Extruded Aluminum Alloy

This paper investigates the fatigue characteristics of a new extruded aluminum 7175, with an experimental composition which uses a magnesium-calcium alloy during the alloying process instead of the standard pure magnesium. This new aluminum 7175, dubbed aluminum ECO7175v1, results in a cleaner manufacturing process and improves mechanical properties. The fatigue behavior of the new aluminum ECO7175v1 T74 temper is investigated. Experimental data show that the fatigue life of ECO7175v1-T74 aluminum can exceed 107 role= presentation style= box-sizing: border-box; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; padding: 0px; margin: 0px; position: relative; \u3e107107 cycles with a fatigue strength of approximately 207 MPa, about 36% of its tensile strength. Fractography results show that failure modes are predominately ductile near the surface and brittle toward the center. In addition, at higher stresses, crack initiation points are typically at the surface of the specimens, compared with those at lower stresses. Irrespective of the stresses to which the specimens are subjected, all crack initiation points are located at the surface and no inclusions to act as stress concentrators are seen

Fatigue Behaviors of Newly Developed Eco-7175-V3 Extruded Aluminum Alloy

Abstract In this study, the fatigue characteristics are evaluated for a new extruded aluminum 7175 with an experimental composition that uses a magnesium-calcium alloy during the alloying process instead of the standard pure magnesium. Specimens of ECO-7175-v3 were fabricated and subjected to fatigue life testing, fatigue life data analysis, and observation of their fracture characteristics through optical microscopy and scanning electron microscopy (SEM), and metallography to study their grains and surface characteristics. The S-N curve shows that the fatigue life for the new fabricated ECO-7175-v3 aluminum can exceed 5×107 cycles, with a fatigue strength of approximately 220 MPa or less, about 40% of its tensile strength. The fatigue strength of ECO-7175-v3 is an improvement over ECO-7175-v1, which is also shown by its higher fatigue strength coefficient, σ′F, of 1,589.7 MPa. When ECO-7175-v3 specimens were subjected to stresses of up to 67% of the ultimate tensile strength (UTS), the fracture surfaces are shown generally to have softly defined fracture features and propagation bands. These fracture surface characteristics are unique to ECO-7175-v3 and are attributed to its larger average grain size. Irrespective of the stress amplitude, like ECO-7175-v1, all crack initiation points of all specimens are seen at the surface and no inclusions to act as stress concentrators are seen. Reliability analysis shows the hazard rates for ECO-7175-v3 remain relatively constant most of the time before increasing towards the end. The trend of the hazard rates indicates failures are due to wear-outs and not due to defects. Reliability analysis also shows that at any given fatigue life cycle and stress level, ECO-7175-v3 has a lower probability of failure compared to ECO-7175-v1

Transmission electron microscopy and thermodynamic studies of CaO-added AZ31 Mg alloys

We investigated the microstructural evolution of Mg-3Al-1Zn (AZ31) alloy systems, with Ca or CaO added, by carrying out microstructural characterizations in conjunction with thermodynamic calculations. A calculated phase diagram of the Mg-Ca-O ternary system showed that CaO can be dissolved in liquid Mg so as to have 12.6 wt.% Ca content in the liquid Mg at 700 degrees C. Therefore, for a 0.3 wt.% CaO-added AZ31 alloy, our thermodynamic calculation predicted a similar precipitation pathway to that of a 0.3 wt.% Ca-added AZ31 alloy during the solidification process. In fact, a thermodynamic analysis of the precipitation pathway assuming the Scheil model showed that the major precipitates in both alloys were Al8Mn5, CaMgSi, Laves C15 and Laves C36, in good agreement with our experimental observation. However, a microstructural characterization of the as-cast alloys using transmission electron microscopy revealed that the spatial distribution of the precipitates was significantly different in the two alloy systems; unlike in the Ca-added AZ31 alloy, the Ca-containing precipitates in the CaO-added AZ31 alloy exhibited strong agglomeration tendencies. Moreover, in an alloy solidified at a faster cooling rate, undissolved CaO particles were observed in the precipitate agglomerates that were connected to the other Ca-containing precipitates. These results suggest that an incomplete dissolution of CaO particles in the liquid results in the agglomeration of precipitates, as the undissolved CaO particles can act as local sources, supplying Ca to the liquid, and can thus act as preferential nucleation sites for the Ca-containing precipitates forming during the solidification of the alloy. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.X112723sciescopu