M. Sobhy

Effect of Zn addition on steady state creep characteristics of Sn–3·3Ag solder alloy

Abstract The materials used in the present study are Sn–3·3 wt-%Ag and Sn–3·3Ag–1Zn (wt-%) alloys. Effect of stress σ, aging temperature T a and aging time t a, on the creep resistance of the alloys under investigation had been studied. Creep tests were performed at room temperature (300 K) under the effect of different constant loads ranged from 2·5 to 4 N on specimens pre-aged at the temperatures 353, 373, 393 and 413 K. At each aging temperature the specimens were heated for the different periods of time 1, 20 and 50 h. The steady state creep rate of the present alloys was found to be related to the applied stress with exponent n. This exponent was found to be decreased with increasing aging temperature T a and/or time of aging t a. Addition of 1 wt-%Zn to the binary Sn–3·3 wt-%Ag solder alloy affected its creep resistance. It was found to decrease with increasing both T a and/or t a. This was attributed to coalesce and enhancement of the particle sizes of the intermetallic compound Ag3Sn during aging at high temperatures (0·6–0·7T m) which subsequently led to the decrease in the pinning action of these particles and consequently leading to decreasing the creep resistance in the aged alloy. Moreover, increasing T a and/or t a increases the coarsening rate of grain sizes in both solder alloys from which it can be considered as another reason for the softening effect of increasing T a and/or t a. Microstructural changes were investigated by optical, electron microscopy and X-ray diffraction measurements.

Effect of adding cobalt on mechanical and structural properties of Cu–2Be alloy aged below half its melting temperature

Abstract The present study mainly covers the effect of adding cobalt on the mechanical and structural properties of Cu–2Be alloy. The stress–strain technique has been employed to investigate the effect of aging time and testing temperature on the work hardening characteristics of Cu–2Be and Cu–2Be–0·3Co alloys aged below half its melting temperature. The obtained results have been discussed based on the structural changes resulted during the aging process.

Resistometric study of Al-10% Zn aged below and above half of the melting temperature

Abstract Ageing characteristics of the alloy Al-10 wt% Zn have been investigated in the temperature range 110–230°C (below and above 0.5 T m ) by resistivity measurements. With time of ageing, the resistometric study delineated two distinct stages: the first stage characterized by a decrease in resistivity, whereas an increase was observed in the second stage. The decrease in resistivity ϱ t with time t at the different ageing temperatures was interpreted as due to the formation and growth of GP zones, while the increase in ϱ t was attributed to the dissolution of the GP zones to form the rhombohedral transition phase which was emphasized by electron microscope investigation. The activation energy of GP zone formation and growth was found to be 0.5 eV in accordance with that quoted in literature.