Superheating

Vol. 19 No. 2

Journal of Wuhan Universityof Technology- Mater.Sci. Ed.

June 2004

Influence of Elemental Iron on Hydrogen Content in Superheated Aluminum-iron Melts *
HU Li-na BIAN Xiu-fang ANANDA Mahto DUAN You-feng

Shandong University
iron has been determined in the temperature range from 973K to 1103K. The hydrogen content in molten A1-Fe alloys increases remarkably when thetemperature of the melt rises to about 1053K. Th/s work indicates that the alloying element iron plays an imtxTtant role in hydrogen content in superheated A1-Fe alloy melts below about 1053K. The results make it clear that the hydrogen content in the melt aluminwn reduces with the increasing element levels. A conclusion is drawn that the degree of gassing in molten Al- Fe alloys is bound up with theproperties of oxide film of aluminum alloy melts. The element iron has no effect on the compact structure of oxide film in aluminum melts. The effects of alloying element are theoretically analyzed in terms of Wagner interaction parameter. According to the valnes of the first order interaction parameter, it is concluded that the interaction between iron atom and aluminum is much stronger than thatbetween hydrogen atom and aluminum, and the addition of the alloying element decreases the ~ n i t y of liquid aluminum for hydrogen. Key words: alumirmm-iron alloy ; hydrogen ; interaction parameter ; oxide film

( Received: May 11,2003 ;Accepted: March 11,2004) Abstract: The hydrogen content in liquid binary aluminum alloys with 1,3,5 and 8 wt%

1

Introduction

melting point and about300~ above, the hydrogen solubility is doubled for each 100 to 120~ increase in superheat E4] . It is,however, very rare for normally produced melts to contain these levels of H [7) , because in production the hydrogen pressure above the melt is low and the oxide film readily formed on the alloy surface acts as a barrier isolating the melt from the atmosphere to impede excessive hydrogendissolution. Besides, comparing with 2-4 hours of holding time needed for the obtained equilibriumIsJ , the holding time in practical foundry is usually less than half an hour. So the investigation on the hydrogen content under unequilibrium conditions is as important as that on the hydrogen solubility at equilibrium. The former is practically critical to the practical control and amelioration of theprofound, and usually deleterious, effects of hydrogen on the physical and mechanical properties of metal products. Few reports have investigated the effects of the element iron on the hydrogen content in liquid aluminum. Talbot et al once thought the hydrogen solubility decreased linearly with the increasing iron content[91 . So far the relatively detailed effects of iron on hydrogen content are stilllack. Concerning that iron is the dominant impurity in commercial grades and is a major impurity in purer grades, and, sometimes, is added to the alloys as a positive element to improve some properties, studies on the element are very important. In this paper the influence of the element iron on the hydrogen content in molten aluminum was studied from both theoretical and experimental aspect.Because of the large numbers and the complexity of aluminum alloys which may contain many elements with different concentrations, a systematic study of the effects of the elements and their interactions on the hydrogen behavior in the alloys would be a very difficult and enormous, but imperative task. Since 1930' s, a lot of investigations have been focused on the solubility of hydrogen in purealuminum and aluminum alloys. Baukloh et al studied the effects of copper and silicon additions on the hydrogen solubility in aluminum[~-~1and Anyalebechi et al studied the hydrogen solubility in liquid binary A1-Li alloys[51 . Besides the elements mentioned above, there are also reports on the hydrogen solubility of other elements such as manganese, magnesium, and titaniumI61 . It is found that...