Papers by Keyword: AA7075-T6

Abstract: Rolled 7xxx-series Al alloys exhibit pronounced microstructural anisotropy (pancake grains and particle stringers) that can strongly affect fatigue initiation and-crack growth. In the current study, an AA7075-T6 plate was examined in three orthogonal machining orientations—L–S (longitudinal), L–T (long-transverse) and T–S (short-transverse)—using high-cycle three-point bending fatigue at room temperature (R = 0, f = 25 Hz, σ_max = 360–400 MPa, i.e., ~0.79–0.88σ_y). Optical/SEM observations reveal elongated grains and a grain-density gradient through thickness, accompanied by orientation-dependent distributions of intermetallic particles. Despite only small differences in monotonic response, fatigue performance is strongly orientation-dependent: the T–S specimens exhibit the longest lives in the S–N curves. Fractography and striation-based kinetics show the lowest Paris-regime crack-growth rate for T–S (da/dN ≈ 1.85×10⁻⁷ m/cycle at ΔK ≈ 10.5 MPa√m), while L–S shows the fastest growth (da/dN ≈ 4.3×10⁻⁷ m/cycle at ΔK ≈ 13.0 MPa√m). The improved T–S fatigue resistance is discussed in terms of crack-path interaction with grain boundaries and particle populations (coherent/penetrable vs non-coherent/coarse particles), which can either deflect/retard cracks or act as initiation sites. The results provide a compact microstructure–mechanics map for rolling-induced anisotropy in AA7075-T6 under bending fatigue.

Abstract: Friction stir welding (FSW) is often preferred for joining aluminium and other lightweight metals in the square butt and lap configurations. The present work focuses on studying the interfacial temperature variation along and transverse to the weld direction during friction stir lap welding (FSLW) of AA7075-T6 mounting the thermocouples on both the advancing side (AS) and retreating side (RS) of the joint during FSLW of 3 mm thick plates using two different pin lengths. The peak temperature noted at the starting, middle, and end of the weld length is consistent, thus suggesting a steady heat generation during the process. However, there is an asymmetry in temperature distribution at the AS and RS of the joint, and the temperature recorded on AS is higher than RS. The peak temperature at a location reaches after a delay of the tool passes, suggesting a variation between the leading and trailing sides. The peak temperature for the joint obtained with the 4 mm pin length is around 40-50 °C higher than the joint with 3 mm pin length.

Abstract: The objective of this study is to quantify and understand the effectiveness of a hexavalent chrome replacement ion to inhibit environmentally assisted fatigue crack propagation (EFCP) in high strength aluminum alloys. Addition of molybdate (MoO4 2-) to bulk-low chloride solution effectively inhibits EFCP in peak aged 7075, comparable to that of CrO4 2-. The effectiveness of inhibition depends strongly on loading variables: .K, R, and frequency as explained qualitatively by mechanical instability of a crack tip passive film that otherwise hinders production and uptake of embrittling hydrogen. The critical loading frequency (and crack tip strain rate), below which film stability and inhibition occur, increases with increasing inhibitor concentration, but only for low stress ratio loading, perhaps due to occluded crack transport and reaction considerations. Molybdate could be a beneficial replacement for chromate and a candidate for inhibitor release from a tailored coating.

Abstract: By contrast with static fracture toughness determination, the methodology for dynamic fracture toughness characterization is not yet standardized and appropriate approaches must be devised. The accurate determination of the dynamic stress intensity factors must take into account inertial effects. Most methods for dynamic fracture toughness measurement are experimentally complex. However, dynamic fracture toughness determination using strain measurement is extremely attractive in terms of experimental simplicity. In this study, dynamic fracture toughness tests using strain measurement are performed. High rate tension and charpy impact tests are carried out for titanium alloy, maraging steel and Al alloys. In the case of evaluating the dynamic fracture toughness using high rate tension and charpy impact tests, load or energy methods are used commonly. The consideration about inertial effects is essential, because load or energy methods are influenced by inertia. In contrast, if the position for optimum response of strain is provided, dynamic fracture toughness evaluation using strain near crack tip is more accurate. To obtain the position for optimum response of strain, a number of gages were attached at angles of 60°. Reliability for experimental results is evaluated by Weibull analysis. The method presented in this paper is easy to implement in a laboratory and it provides accurate results compared to results from load or energy methods influenced by inertia.