Aspects of the phase transformation during aging of Zn-11% Al and Zn-27% Al alloys

peer reviewedThe purpose of this work is to study the complex evolution observed during aging and the effect of alloying elements in ZA12 and ZA27. The results confirm the existence of the cellular reaction which appears very quickly: after 1 h at 100 deg C the quench alpha sub 1 phase has nearly decomposed and the lamellae have begun to appear. Evidence of the second stage of aging is shown by the aged Zn--10.2% Al which exhibits fine precipitates alpha ' sub m FCC in alpha ' lamellae. When the aging time is increased diffusion of Zn inside these particles increases the difference in crystalline parameters leading to alpha ' HCP precipitates and finally to eta HCP. The aging is completed when the fine microstructure alpha ' sub m has disappeared leading is large globular grains of alpha and Bet

Quantitative X-ray microanalysis of precipitates in zinc-aluminium-copper

peer reviewedThe aim of the present study is to adapt the Cliff-Lorimer method for quantitative analysis of thin foils and to obtain information about the composition of fine metastable precipitates in Zn-Al-Cu alloys. The coefficients K(al-zn) and K(al-cu) were determined for accelerating voltage of 200 kV, about which there has no been data ever mentioned. Some applications of the method are given

Phasenbildung wàhrend der Auslagerung von Zn-12 Gewr% AI- und Zn-27 Gewr% AHegierungen bei 1oo°C

peer reviewedaudience: researcher, professional, studentThe phase formation during ageing of ZrH2 wt% AI and Zna27 wt.% AI alloys at 100 O has been studied by means of transmission electron microscopy and electron diffraction. No formation of ellipsoidal precipitates of GP 2 and c4 phase bas been observed. Precipitation of hexagonal phases occurs generally on account of the a phase. The habitus plane of a new phase q has been found. The q phase has been distinguished from the metastable Qm using Moire patternsDie Phasenbildung wâhrerid der Auslagerung von Znel2 Gew:% AF und Zn-27 Gew:% Al-Legierungen bel wurde durchstrahlungselektronenmikroskopisch untersucht, Es wurde keine Bildung der elliptisohen Ausscheidungen GP 2 und der c4-Phase beobachtet. Die Ausscheidung hexagonaler Phasen erîolgte auf Kosten der c4-Phase. Die Habitusebene (011) einer neuen Phase q wurde gefunden; diese q-Phasé IieB sich von der metastabileriqm-Phaée durch ein MoireeMuster unterseheiden

Microstructural study of Zn-11% Al and Zn-27% Al alloys

Zinc-aluminium alloys with small amounts of copper and magneisum (ZA alloys) are used in a number of casting processes. They offer the foundry industry a family of zinc alloys with a wide range of mechanical properties able to meet a large spectrum of performance criteria. However promising the characteristics of these alloys, microstructural studies of them are incomplete. It has been shown that copper additions to ZA alloys modify the number of the phase existing in the binary zinc-aluminium system as well as their transformation kinetics. Microstructural studies have shown not only the heterogeneity of the microstructure but also the presence of a zinc-rich metastable phase and the evolution of the composition of the ternary phase Zn-Al-Cu (T) during ageing. This situation is not surprising as several studies have shown the existence of metastable phases in the binary system Al-Zn with high aluminium content. the complexity of the microstructure leads us to search further for a better understanding of the binary Zn-Al alloys, with Al contents corresponding to ZA 12 and ZA 27 wihout any Cu and Mg, in order to precise about the complex evolution to stable phases observed in these alloys

Review of hot shortness problems in copper-containing steel

The problem of hot shortness is first briefly discussed in terms of the recycling of scraps and the occurrence of various residual elements in steel. The phenomenon is then defined and described as a function of the factors influencing its different stages : copper solubility in austenite, copper phase melting point, wettability of the liquid copper rich phase, oxidation, furnace atmosphere, occlusion and diffusion. The effect on these phenomena of other residual or alloying elements is discussed. The paper concludes with the different ways to minimize the hot shortness problems and with hints on the more efficient use of copper containing scraps

Microstructural study of Zn-Al alloy

It is well known that zinc-aluminium alloys posses very good mechanical properties. This is the reason why the investigation of their ageing characteristics is very important for the practice. Several solid state reactions between alpha, beta, epsilon and T phases have been established for such materials alloyed with copper, but there has been no detailed on the formation, development and transformation of metastable phases into stable ones. This is exactly the aim of our investigation