EFFECT OF ELECTRON BEAM PROCESSING ON MECHANICAL PROPERTIES OF ALUMINUM ALLOY 7075

NOIKJO

Abstract

The mechanical properties of aluminum alloy grade 7075 modified by electron-beam processing were studied. The samples were subjected to two types of mechanical tests: uniaxial tension at a constant rate and fatigue loading. The state of the elemental and phase composition of the Al-Zn-Mg-Cu alloys was studied using scanning electron microscopy. In the AA7075 alloy after electron-beam modification, the main role is played by the α-Al matrix, in which the alloying elements Zn, Mg and Cu, as well as Fe, Si and Mn are in solid solution. With a local increase in the concentrations of Zn and Mg, the strengthening η-phase (Mg(Zn,Cu)₂) is formed, and in the presence of Cu and Mg, particles of the S-phase (Al₂CuMg) are released. In areas with high copper content (≥ 35 аt. % Cu) and the presence of Fe/Ni, θ-phase intermetallic compounds (Al₂Cu) and complex Al–Fe–Ni–Cu compounds are formed, whereas individual areas with a predominance of Zn and Cu (28–46 at. % Zn, 27–40 at. % Cu) are characterized by the presence of Cu–Zn intermetallic compounds. Electron beam processing (EBP) of 7075 aluminum alloy obtained by the additive method increases the ultimate strength by 2 times (from 100.9 to 199.3). This is achieved by eliminating defects, microstructural changes, and relieving residual stresses from layer-by-layer deposition during additive manufacturing. After fatigue testing, the additively manufactured sample demonstrates ≈235,000 cycles before failure (versus 130,000 for the traditional analogue), and the combination with EPO increases the endurance to 260,000 cycles. The standard deviation of σ ≈ 5–8 % for strength, σ ≈ 10–15 % for fatigue confirms that the electron beam processing method eliminates the disadvantages of additive manufacturing, providing a simultaneous increase in strength, ductility and fatigue life of the 7075 alloy.