Search

The properties of Al–Li alloys have been extensively studied recently for structural applications in automotive and aerospace industry, thanks to their lower density and enhanced modulus of elasticity. In common with many Al alloys, one of the main issues is the loss of toughness and soundness of welded joints consequent upon welding operations, in particular, possible cracking in the weld metal and metallurgical modifications induced in the heat-affected zone. In this work, welding trials were carried out on 8090 Al–Li plates welded by electric arc, using a 5% Mg filler metal. Joints were mechanically and metallurgically characterized through tensile and microhardness tests, optical and scanning electron microscopy, and fractography on both welded and unwelded tensile specimens. Energy dispersive spectroscopy (EDS) measurements were also performed to evaluate chemical composition locally and determine the nature of precipitates.

The aim of this paper is the study of the influence of addition of Si, Ni and Co on the microstructure and mechanical feature of Is-ct gold alloys, in order to reduce production rejects in the investment cast process. For this reason, a typical alloy containing Ag, Cu and Zn usually used for jewelry manufacturing, has been used to prepare four master alloys with variable concentrations of Si, Co and Ni; 18-ct gold alloys were also prepared. It has been demonstrated that the increasing of Si concentration induces embrittlement in gold alloys. XPS analysis on fractured samples revealed the presence of SiO2 at the grain boundaries of samples containing 0.25 wt.% of Si. The addition of Ni and Co permitted to obtain gold alloys with good mechanical properties and surface finishing. It has been also demonstrated that Ni and Co form insoluble intermetallic compounds with Si that decrease SiO2 content at the grain boundaries thus preventing embrittlement. XRD analysis permitted to identify the compounds as Ni3Si and Co2Si. (C) 2001 Elsevier Science B.V. All rights reserved.