Heat Sink Effect on 6061 Aluminum Alloy Welds with Different Partial Aging Conditions
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Heat Sink Effect on 6061 Aluminum Alloy Welds with Different Partial Aging Conditions C.M. Go´mora, R.R. Ambriz, J. Zuno-Silva, and D. Jaramillo1 (Submitted December 9, 2019; in revised form June 18, 2020) Partially aged 6061 aluminum plates were welded by the gas metal arc welding process. During the welding process, a cooling system to act as a heat sink was used to extract the heat coming out from the welding process. To determine the experimental weld thermal cycles, K type thermocouples were placed at the heat affected zone. Finite element was used to compute the thermal distribution and isothermal sections generated by welding. The temperature measurements, Vickers microhardness profiles and tensile tests were observed to be related with the microstructural β″ to β′ phase transformation. The over-aging of the heat affected zone tends to diminish when the heat sink is used as compared with the reference welding condition. An increase on tensile strength (about 5.8%) and ductility (close to 29%), for welds performed in partial aging materials with respect to the welds with artificial aging condition (6061-T6 alloy) was also observed.
Keywords
6061 aluminum alloy, experimental and numerical thermal cycles, heat sink, microstructural transformation, tensile mechanical properties
1. Introduction 6061 aluminum alloy is hardened by solution and precipitation heat treatment (artificial aging), reaching a mechanical strength of approximately 310 MPa in a T6 condition. Due to its ratio between strength and density, this alloy is commonly used in the transport industry. However, when welded, the heat input generated by the processes induces microstructural transformations of the Mg2Si intermetallic at the heat affected zone (HAZ) (Ref 1). This phenomenon promotes a decrease in yield and ultimate tensile strength of the welded joints. The mechanical properties and metallurgical changes for 6061-T6 aluminum alloy welds were reported initially by V. Malin (Ref 2). This author used hardness measurements and analytical weld thermal cycles to evidence a soft zone formation in the HAZ. He also observed that the failure, after tensile test, was located at the HAZ, where the peak temperature during the weld thermal cycle reaches about 380 °C with a dwell-time of approximately 10 s. This was attributed to the over-aging process which transforms the coherent β″ to the incoherent β′ phase. The over-aging phenomenon of the HAZ can be reverted by means of post-weld heat treatment (PWHT). For instance, Fadaeifard et al. (Ref 3). and Ambriz et al. (Ref 4) carried out an artificial aging treatment after welding of a 6061-T6 C.M. Gómora and J. Zuno-Silva, Universidad Autónoma del Estado de Hidalgo, Escuela Superior de Ciudad Sahagún, Carretera Cd. Sahagún-Otumba S/N, zona industrial, Cd. Sahagún, C.P. 43990 Tepeapulco, HGO, Mexico; R.R. Ambriz and D. Jaramillo, Instituto Politécnico Nacional CIITEC-IPN, Cerrada de Cecati S/N Col. Sta. Catarina, Azcapotzalco, C.P. 02250 Ciudad de México, Mexico. Contact
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