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Abstract Magnesium alloys, which are the lightest engineering structural material, have been more-widely used
in various industries, such as transportation, aerospace, computers, home appliances, communications and medical
care, etc., owing to their desired performance of low density (~1.74 g/cm3), high specific strength, high specific
stiffness, excellent casting, good electromagnetic shielding, damping, biocompatibility, weldable and machinable,
and so on. Magnesium alloys have been honoured as the 21st century green engineering materials by many scientists
and engineers. However, our country is still at the level of a large country of magnesium raw material, and the
majority of magnesium resources are exported to other developed countries as raw materials at very low prices.
Therefore, it is of great significance to carry out in-depth research on magnesium alloy and its products, so as to
transform China from a big country of magnesium raw materials into a powerful country of magnesium alloy products,
and promote the transformation of resource advantage into economic advantage. In addition, compared with
forged magnesium alloy, cast magnesium alloy, in which 90% magnesium alloy is prepared by the casting method,
has been widely used in many fields due to its low production cost and mass production. Up to date, the most representative
cast magnesium is AZ91, and it has a market share of more than 50%. Furthermore, the microstructure of
as- cast AZ91 magnesium alloy consists of dendritic α- Mg solid solution, net- like β- Mg17Al12, Mg2Si and
Al8Mn5, so the mechanical performace is lower than that of aluminum alloys. Meanwhile, the magnesium element
is easy to be corroded and out of operation in harsh environment because it is very active and its electrode potential s very low (about -2.36 V), so the corrosion of magnesium alloy restricts its extensive application and industrialization.
Among a lot of methods, alloying is one of the effective methods to improve the microstructure, refine grain
size and enhance mechanical property and corrosion resistance of AZ91 magnesium alloy. In the paper, the effects
of single alloying (such as As, Ca, Sm, Zr, Nd, Sc, Y, CaO, etc.), composite alloying (such as Ca-Y, Nd-Ca, Ce-La,
etc.) and master alloy (such as Mg-Al-C, Al-TiB2, etc.) on the microstructure, mechanical property and corrosion
resistance of AZ91 magnesium alloys are reviewed and analyzed. The current results shown that the beneficial effects
of composite alloying are the most significant, but there is no theoretical basis to direct the doping amount.
Therefore, in order to provide reference for the development of high-performance AZ91 magnesium alloy, it is suggested
to develop the corresponding composite alloy system based on material genetic engineering and reveal its
mechanism, and the mapping relationship between alloying element content and microstructure, properties of AZ91
magnesium alloy should be disclosed in the future.
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2022, Vol. 32 
