ML5 alloy structure and properties at different modification methods

A factor exerting a decisive influence on the complex of mechanical, technological and operational properties when making castings of magnesium alloys with a wide crystallization range is the casting structure. It is impossible to obtain a required structure of Mg— Al—Zn alloys without melt modification in the melting process. The paper provides the results obtained when studying the process of ML5 magnesium alloy modification with various substances. The influence of 0,4—0,45 wt.% magnesite introduced in the melt at a temperature of 720—740 °C was studied, as well as the influence of melt purging with oxygen-free carboniferous gases at the same temperature on the structure of the obtained alloy and the time of modification effect retention. The latter is especially important in large-lot and mass production of small Mg—Al—Zn—Mn alloy castings for a long time when melt pouring into molds takes considerable time. It is shown that oxygen-free carboniferous gases used for ML5 alloy modification ensure mechanical properties of castings 15 — 20 % higher than the standard level according to GOST 2856-79. The efficiency of retaining the effect of modification using the standard method (magnesite) and with oxygen-free carboniferous gases is compared. It is shown that the effect of modification with magnesite remains within no more than 30—40 minutes, while the effect of modification with oxygen-free carboniferous gas remains not less than 4 hours that enables long pouring of alloy into molds.