Corrosion Performance and Mechanical Strength in Aluminum 6061 Joints by Pulsed Gas Metal Arc Welding.

In this paper, the analysis of electrochemical corrosion performance and mechanical strength of weld joints of aluminum 6061 in two-heat treatment conditions was performed. The joints were produced by gas metal arc welding in pulsed mode. The original material exhibited precipitates of ß and ß" phases in a volume fraction (Vf) of 2.35%. When it was subjected to a solubilization process, these phases were present in a Vf = 2.97%. This increase is due to their change in shape and distribution in clusters within the aluminum matrix. After the welding process, the best sample in the solubilization condition reached 117 MPa, while the original material achieved 104 MPa, but all samples showed a fracture in the fusion zone. This is attributed to the heat input that produces high and low hardness zones along the heat-affected zone and the welding zone, respectively. Moreover, the change in microstructure and phase composition creates a galvanic couple, susceptible to electrochemical corrosion, which is more evident in the heat-affected zone than in the other weld regions, exhibiting uniform and localized corrosion, as was evident by electrochemical impedance spectroscopy. The heat from the welding process negatively affects the corrosion resistance, mainly in the heat-affected zone.

Comparative in Mechanical Behavior of 6061 Aluminum Alloy Welded by Pulsed GMAW with Different Filler Metals and Heat Treatments.

Precipitation hardening aluminum alloys are used in many industries due to their excellent mechanical properties, including good weldability. During a welding process, the tensile strength of the joint is critical to appropriately exploit the original properties of the material. The welding processes are still under study, and gas metal arc welding (GMAW) in pulsed metal-transfer configuration is one of the best choices to join these alloys. In this study, the welding of 6061 aluminum alloy by pulsed GMAW was performed under two heat treatment conditions and by using two filler metals, namely: ER 4043 (AlSi5) and ER 4553 (AlMg5Cr). A solubilization heat treatment T4 was used to dissolve the precipitates of ß"- phase into the aluminum matrix from the original T6 heat treatment, leading in the formation of ß-phase precipitates instead, which contributes to higher mechanical resistance. As a result, the T4 heat treatment improves the quality of the weld joint and increases the tensile strength in comparison to the T6 condition. The filler metal also plays an important role, and our results indicate that the use of ER 4043 produces stronger joints than ER 4553, but only under specific processing conditions, which include a moderate heat net flux. The latter is explained because Mg, Si and Cu are reported as precursors of the production of ß"- phase due to heat input from the welding process and the redistribution of both: ß" and ß precipitates, causes a ductile intergranular fracture near the heat affected zone of the weld joint.

Resultado perinatal del embarazo múltiple con un protocolo estándard de tratamiento / Perinatal result of multiple pregnancy with a standard protocol of treatment

Se presentan los resultados obtenidos en un grupo de 36 pacientes con embarazo múltiple, en las que se instituyó un protocolo de manejo, con objeto de disminuir la morbilidad y mortalidad perinatal. El protocolo consistió en la aplicación de siete diferentes puntos. Con dicho protocolon se obtuvo una disminución en la morbilidad perinatal, en cuanto a lo referente a preclampsia, retardo en el crecimiento intrauterino, parto pretérmino y síndrome de insuficiencia respiratroia neonatal. La mortalidad perinatal en este grupo fue sólo de 3.7%. Se concluye que el manejo estandarizado del embarazo múltiple disminuye importante los riesgos perinatales en dicha eventualidad obstétrica