Recovery of Mechanical Properties of a 6061-T6 Aluminum Weld by Heat Treatment After Welding
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THE 6xxx aluminum alloys are used in the aeronautical, maritime, and ground transportation industries due to their combination of mechanical and corrosion resistance.[1] They present a good balance between strength and density (E/q = 25.5 MPa g1 cm3; ro/ q = 102 MPa g1 cm3) as compared to structural steel ro/q = 38 MPa g1 cm3). (E/q = 27 MPa g1 cm3; Such alloys could be hardened by solubilization and artificial or natural aging to increase their mechanical properties. For instance, the 6061 alloy reaches a yield strength around 280 MPa in the artificial aging condition (T6). However, after welding, the mechanical resistance of the joint (hardness and tensile strength) decreases[2–4] due to an overaging phenomenon (soft zone formation) at the heat-affected zone (HAZ) imposed by the weld thermal cycle. The loss of hardening in welds of the 6061-T6 alloy has been studied in terms of the transformation of the b¢¢ to b¢ precipitates JAVIER SERRANO PE´REZ, PhD Student, and RICARDO RAFAEL AMBRIZ ROJAS and DAVID JARAMILLO VIGUERAS, Professors, are with the Instituto Polite´cnico Nacional CIITEC-IPN, Cerrada de Cecati S/N Col. Sta. Catarina, CP 02250, Azcapotzalco, DF, Mexico. Contact email: [email protected] FRANCISCO FERNANDO CURIEL LO´PEZ, Professor, is with the Facultad de Metalurgia, Universidad Auto´noma de Coahuila (UAdeC), Carr. 57, km 5, Monclova, Coahuila, Mexico. Manuscript submitted July 13, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
according to the precipitation sequence given by Edwards et al.[5] Supersaturated solid solution ðass Þ ! GP zones ! b00 ! b0 ! b The microhardness evolution and local tensile properties for the 6xxx alloy welds have been studied by several authors.[6–11] Ambriz et al.[12] studied the Vickers microhardness map representation of the 6061-T6 welded joints to determine the hardness variation, as well as the identification of different zones of the joints. They found a soft zone in the HAZ with hardness values around 61 HV0.1 (~0.6 GPa) and a yield strength decrement of approximately 50 pct with respect to the base metal. The hardness (~80 HV0.1) and yield strength (133 MPa) for the weld metal tend to improve as compared with the soft zone. The microstructural damage produced by the weld thermal cycle in the HAZ can be reverted by a postweld heat treatment (PWHT) of solubilization and artificial aging (T6). That is to say that the hardening of the HAZ will be similar to that of the base metal. Some studies have been conducted to analyze the PWHT effect on welds of a 6061-T6 alloy.[13,14] For instance, Ahmad and Bakar[15] reported the hardness and tensile mechanical properties in single-V groove joints welded by gas metal arc welding (GMAW) by using the cold metal transfer
method. They found that the average hardness in the weld metal tends to increase from 68.8 to 86.4 HV for the as-welded and PWHT conditions, respectively. However, the tensile strength tends to remain at similar values (53.3 MPa in the as-welded condition and 55.3 MPa for PWHT). In this context, an alternative to wel
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