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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 (AlSi 5 ) and ER 4553 (AlMg 5 Cr). A solubilization heat treatment T4 was used to dissolve the precipitates of β"phase into the aluminum matrix from the original T6 heat treatment, leading in the formation of β-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 β"phase due to heat input from the welding process and the redistribution of both: β" and β precipitates, causes a ductile intergranular fracture near the heat affected zone of the weld joint.

Aluminum alloys are very promising for structural applications in aerospace, military and transportation industries due to their light weight, high strength-to-weight ratio and excellent resistance to corrosion. In comparison to unreinforced aluminum alloys, aluminum/aluminum alloy matrix composites reinforced with ceramic phases exhibit higher strength and hardness, improved tribological characteristics. A novel surface modifying technique, friction stir processing (FSP), has been developed for fabrication of surface composite with an improved performance. The effect of FSP parameters such as number of passes, direction of each pass, sealed or unsealed groove on microstructure was investigated. In this work, nano-particles of TiC (2% in weight) were added to aluminum alloy AA7075-T651 to produce a functional surface. Fixed parameters for this AA7075 alloy were used; rotation speed of 1000 rpm, travel speed of 300 mm/min and pin penetration of 2.8 mm. Optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed to study the microstructure of the fabricated surface composites. The results indicated that the selected FSP parameters influenced the area of surface composite, distribution of TiC particles and micro-hardness of the surface composites. Finally, in order to evaluate rate wear the pin on disk test was carried out. Key-words:Friction Stir Processing (FSP); Nano-particles; Aluminum alloy 7075; Surface composite; Wear. Efeito dos Parâmetros do Proceso de Fricção Agitação para Reforçar Uma Placa de Aluminio Al7075-T651 com TiCResumo: As ligas de alumínio são promissoras para aplicações estruturais nas indústrias aeroespaciais e de transporte devido ao seu elevada relação resistência-peso e excelente resistência à corrosão. Em comparação com as ligas de alumínio não reforçadas e alumínio/compósitos de matriz de alumínio reforçados com fases cerâmicas, exibem maior resistência e características tribológicas melhoradas. Foi desenvolvida uma técnica de modificação superficial, friction stir processing, para a fabricação de superfície de compósitos. Foi investigado o efeito dos parâmetros FSP como número de passes, direção de cada passe e ranhura selado ou não selada. Neste trabalho, nanopartículas de TiC (2% em peso) foram adicionadas à liga de alumínio AA7075-T651 para produzir uma superfície funcional. Foram utilizados parâmetros fixos para a liga AA7075: velocidade de rotação de 1000 rpm, velocidade de deslocamento de 300 mm/min e penetração do pino de 2,8 mm. Microscopia óptica (MO), microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM) foram utilizadas para estudar a microestrutura. Os resultados indicaram que os parâmetros FSP selecionados influenciaram na área da superfície do compósito, na distribuição de partículas de TiC e na microdureza da superfície. Finalmente, a fim de avaliar a taxa de desgaste o teste de pino sobre disco foi realizado. Palavras-chave:Processamento por Fricção Agitação (FSP); Nanopartículas; Liga de ...

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Plasma Transferred Arc (PTA) process is increasingly used in applications where enhancement of wear, corrosion and heat resistance of metals surface is required. The shape of weld bead geometry affected by the PTA welding process parameters is an indication of the quality of the weld. PTA is a versatile method of depositing high-quality metallurgically fused deposits on relatively low cost surfaces. The overlay deposited is an alloy that is hard and more corrosion resistant than counterparts laid down by Gas Tungsten Arc Welding (GTAW) or Oxy Fuel Welding (OFW) processes. Weld deposits are characterized by very low levels of inclusions, oxides, and discontinuities. This process produces smooth deposits that significantly reduce the amount of post weld machining required. Metal-Mechanic industry continuously requires recovering tool steel components subjected to severe wear. The steel known as D2 is considered to be a high carbon, high chromium cold work tool steel. In this research, weld beads were deposited on D2 steel by using PTA process with different parameters as welding current and travel speed using base nickel filler metal. In order to evaluate the metallurgical features on the weld beads/substrate interface a microstructural characterization was performed by using Scanning Electron Microscopy (SEM) and to evaluate the mechanical properties was conducted the wear test.