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In this paper the fatigue damage accumulation under block program loading is investigated. Alternative flexion bending fatigue tests with a single change in stress amplitude are performed at room temperature for step-down sequence with two-step and threestep loading. The fatigue strength of aluminum 7050-T7451 alloy under block loading is investigated through comparison between the remaining cycles and consumed cycles ratios. The experimental results from the blocks loading fatigue tests are compared with the predictions using Miner's rule. It is shown that, two-step the fatigue strength is enhanced for smaller consumed fatigue loading and the cumulative fatigue damage calculated in accordance with the LDR, for three-step the fatigue strength occurs to a higher number of consume fatigue loading and the LDR rule trend to underestimate the fatigue life and the accumulative damage becomes higher than unity.

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The quantification of nanometric precipitates in Al-Zn-Mg-Cu alloys has been performed by a series of experimental techniques. Especially in the AA7050 alloy, after ageing heat treatment, the particles responsible for the hardening become very thin. Typically, these precipitates of nanometric sizes are mainly characterized by transmission electron microscopy (TEM), which in this particular case, requires a very meticulous preparation. This study investigated a possible alternative quantification of the precipitates by atomic force microscopy (AFM) to complement the technique by TEM. For this, three conditions for heat treatment of an aged aluminium alloy AA7050 were therefore chosen to produce different density and sizes of precipitates. The experimental results showed that the AFM technique proved to be a valid qualitative tool and may complement the results obtained by TEM an exploratory analysis for the microstructures.

The friction surfacing process of two deposited layers on two deposition surface conditions, i.e., a smooth interface and a rough interface, was investigated. The control parameter of the deposition process was the rod feed rate with the use of a conventional milling machine. Analyzes of the surface characterization and microstructural characterization along the produced deposits were performed. The interface strength of the substrate/deposit1 (smooth) and deposit1/deposit2 (rough) was evaluated by bending tests and the micro-hardness profile along the transverse section of the substrate/deposit1 and deposit1/deposit2. The bending tests revealed the presence of smalls delaminations with no evidence of fracture at the rough deposit1/deposit2 interface (D1/D2) with less predominance in the deposition condition 3B. This suggests that the combination of the travel speed of 5.5 mm/s and an increase in the consumable rod feed rate of (≥5.5 mm/s) increases the adhesive strength of the two produced interfaces.

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