The Study Of Microstructure Heredity Of ZAlSi7MgY Alloy

Many problems on casting quality to a great extent are originated from the quality of raw metal material, because the microstructure of raw alloy material takes direct effect to the microstructure of later alloy product, which is the problem now needed to be solved by gene engineer of metal also named heredity of metal microstructure. Now as a new subject either in theory or in technology, it takes great significance for improving casting quality, promoting alloy properties, and plotting reasonable technology.In this paper, focused on the study of heredity phenomenon of an aluminum alloy ZAlSi7MgY, several methods were adopted to investigate the heredity of this alloy microstructure, and then the overall properties of ZAlSi7MgY were improved by the heredity principle. The results are as follows:In general cast condition, the microstructure of mother alloy can obviously transmit to child alloy after remelt, which means that, without special treatment, if the grain of mother alloy is coarse, the grain of remelt alloy is also coarse; if the grain of mother alloy is fine, and the grain of remelt alloy is also fine. The heredity of mother alloy can only exist under certain conditions, if the melt was specially treated, the heredity will damage. When ZAlSi7MgY alloy was superheated to 820～865℃, the morphology of Si phase was changed into a structure.Like that of the phase after modification, and -Al also was fined, overall, the morphology of the mother alloy was improved. However, if by remelting, the mechanical properties have little change, but by superheated at 865℃, the alloy has the best overall mechanical properties.Based on heredity of ZAlSi7MgY alloy, by adding a certain quantity of thin plates, being made from forging liquid alloy, to melt, the casting grain can be effectively refined; but with the delay of the time of the temperature holding, the refining effect is gradually reduced and vanished. Adding a certain quantity of thin plates can also obviously improve mechanical properties, for example, in the paper, after adding 10% thin forging plates into the melt, and keeping 20 minutes,σb was increased 25%, and 50%. In ZAlSi7MgY melt, the atom cluster with the feature tending to form into fine grain is unstable, and is to decompose as the temperature is keeping for a long time. And when the size of the atom cluster goes smaller than a certain number, the heredity will die down.With the cooling rate increases from 25℃/s to 80℃/s then to 260℃/s, the grain size will decrease, and the morphology of Si in eutectic phase be fined, and disperse more even.When treated by solid solution strengthen at 545℃, ZAlSi7MgY alloy have either good strength or good ductility. In the course of solid solution treatment, the morphology change will take place both for Si phase and Fe phase which will turn their shape from needlelike into spherelike. If increasing solid solution temperature or delay the temperature holding time, the shape of Si phase and Fe phase are more rounder, so that its mechanical properties are surely increased, especially its elongation. On the whole, the harmful heredity may be removed through solid solution.The microstructure heredity of metal or alloy are affected by melt technology (say melt temperature or temperature holding time), treatment technology for melt (superheat or changing cooling rate, etc), and other technological factors. Such technological conditions can alter the solidification conditions to alter the microstructure and properties of castings.