The Role of cobalt and nickel intermetallic phases on the mechanical properties and microstructure evolution of Al-Zn-Mg-Cu alloys

• Autor(a) principal: Naeem,Haider Tawfiq
• Data de Publicação: 2014
• Outros Autores: Mohammed,Kahtan Sadeq, Ahmad,Khairel Rafiez
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Materials research (São Carlos. Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392014000600039
• topic: Al-Zn-Mg-Cu alloys; nickel additives; Dispersion; RRA treatments

In this study, the effects of cobalt and nickel additions on microstructure evolution and mechanical properties of Al-Zn-Mg-Cu alloys produced by chill casting process were investigated. Al-Zn-Mg-Cu aluminum alloys containing Ni and Co additives were homogenized at different heat treatment conditions, aged at 120ºC for 24 h, and retrogressed at 180ºC for 30 min then re-aged at 120ºC for 24h. Comparison of the ultimate tensile strength of the Al-Zn-Mg-Cu base alloy underwent RRA temper process with that of the base alloy underwent a similar heat treatment process after the addition of 0.5 wt. % Ni and 0.5 wt. % Co showed that the gains of tensile strengths of the orders of 100 MPa and 135 MPa were attained respectively. These improvements are attributed to phase dispersion particles of the formation of Ni and Co-rich such as Al7Cu4Ni, Al75Ni10Fe15, Al3Ni2 and Al70Co15Ni15. The dispersed particles of nickel or/and cobalt have improved the ultimate tensile strength to reach 630 MPa and 665 MPa and the hardness HV values to 250 MPa and 265 MPa respectively. Besides dispersion, Ni and Co intermetallic dispersoids retarded the grain growth, led to grain refinement and precipitation hardening and resulted in further strengthening of the Al alloy. Microstructure characterization of the alloys was carried out using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD).