Structure and Properties of the ML5 Alloy for Various Modification Methods

Аннотация

When producing castings of wide-interval magnesium alloys, their structure is the factor that most decisively affects a complex of mechanical, manufacturing, and operational properties. The specified structure of alloys of the Mg–Al–Zn system is impossible without using the melt modification operation in the smelting manufacturing process. In this work, the results of studying the modification of the ML5 magnesium alloy by different substances are presented. The influence of introducing magnesite into the melt in an amount of 0.4–0.45 wt % at 720–740°C, as well as the influence of melt blowing by oxygen-free carbon-bearing gases at the same temperature on the structure of the alloy and conservation duration of the modification effect is investigated. The latter is especially important in the large-scale and mass production of small castings made of alloys of the Mg–Al–Zn–Mn system when the melt pouring process is prolonged. It is shown that the use of oxygen-free carbon-bearing gases to modify the ML5 alloy provides the attainment of the level of mechanical properties of castings elevated by the 15–20% level of mechanical properties of castings when compared with the standard one according to GOST (State Standard) 2856–79. The conservation efficiency of the duration of the modifying effect by the conventional method (magnesite) is compared with using oxygen-free carbon-bearing gases. It is shown that the modification effect by magnesite is retained no longer than 30–40 min, while, when using oxygen-free carbon-bearing gas, it is no shorter than 4 h, which makes it possible to perform the prolonged pouring of a melt over molds.