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Effect of Hydrogen on Mechanical Properties of Aluminum AA 6061 Alloy Hardened by Precipitation M. A. Doñu Ruiz1, V. J. Cortés Suárez2, N. López Perrusquia1, L. D. Rosado Cruz3, F. de J. Valencia Jara3, A. Altamirano Torres2 1 Instituto Politécnico Nacional,SEPI-ESIME, Adolfo López Mateos, Zacatenco, México D.F., 07738, México. 2 Universidad Autónoma Metropolitana UAM unidad Azcapotzalco, Departamento de Materiales, Av. San Pablo 180 Azcapotzalco, México .DF, 02200. 3 Universidad Politécnica del Valle de México UPVM. Av. Mexiquense s/n Esquina Av. Universidad Politécnica, Col Villa Esmeralda, 54910, Tultitlan. Edo de México. ABSTRACT The present work reports on the effect of hydrogen on mechanical properties of aluminum AA 6061 hardened by precipitation. Test specimens are solution treated in an electric induction furnace at 803 K during 1 hour and then precipitation hardened during 4 hours at 423, 448 and 473 K. The heat treated specimens are subjected to a hydrogen cathodic charging process during 0, 24 and 96 hours and then tested under monotonic uniaxial tensile loading according to ASTM E8-03. Scanning electron microscopy characterization of tensile fracture surfaces reveals that hydrogen charging of precipitation hardened specimens enhances intergranular cracking by microvoid coalescence and intragranular cleavage fracture. The results show that, although hydrogen charging causes embrittlement of precipitation hardened aluminum AA 6061, the effect is a function of time; short time cathodic charging increases the ductility of the alloy. INTRODUCTION Aluminum alloys containing Mg and Si as major alloying additions are widely used for automotive applications because of their good combination of properties. The heat treatable AlMg-Si alloys of the 6xxx series are often chosen for these applications, since they show a good combination of formability, corrosion resistance and weldability [2]. The hardening phase in these alloys has recently been identified to be the coherent metastable β″ phase [1]. The introduction of hydrogen into aluminum alloy systems generally has a deleterious effect on the mechanical properties and particularly on the fracture toughness [3, 5]. The embrittlement resulting from the presence of solute hydrogen can be induced during processing or service in a gaseous or liquid corrosive environment. Strengthening of Al-Mg-Si alloys is based on a precipitation hardening process [6–8] and numerous investigations have reported on the effect of external hydrogen intake on the deformation and fracture behavior of precipitation hardened alloys[6,7]. The purpose of this work is to evaluate the effect of cathodic hydrogen charging on the mechanical properties and fracture behavior of aluminum AA 6061 hardened by precipitation. EXPERIMENT The nominal chemical composition of the aluminum AA 6061 alloy used in the present study is 0.40-0.80% Si, 0.80-1.20% Mg, 0.7% Fe, 0.15-0.4% Cu, 0.15% Mn, 0.04-0.035% Cr,

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0.25% Zn, 0.15% Ti. Tensile specimens are solution treated at 803 K for 1 hour and quenched