4. Summary and concluding remarksWe

4. Summary and concluding remarksWe have presented a brief review of the recent development of high-strength Mg-RE casting and wrought alloys inthis article. So far reportes indicate that the study of highstrength Mg-RE alloys is mainly foused on Mg-Gd and MgY systems. Here, we make several conclusions and point outsome areas which would be worthwhile for further scientificinvestigation in the future.(1) For developing high-strength Mg-RE alloys, precipitation strengthening is very crucial. The quality of precipitates is distinctly important. A higher strength can beachieved if a high density of nanoscale co-precipitates,i.e. plate-shaped precipitates with both prismatic andbasal habit planes and also large aspect ratio, can bedeveloped in the microstructure. At present, the microstructure of Mg-RE-Zn and Mg-RE-Ag systems contains both prismatic and basal plates. The basal plates insuch a microstructure have a large aspect ratio (γ , γ ,basal SFs or 14H LPSO), and the aspect ratio as well asnumber density of the prismatic plates (β, etc.) is muchlower that typical precipitates formed in high-strengthAl alloys.(2) For developing high-strength Mg-RE alloys, it isequally important to develop the methods and technologies to realize refining grain size of the α-Mg matrixdown to the submicron or even nanometer scale to fulfillthe grain refinement strengthening.(3) Realizing the full potential and making the full advantages of LPSO/SFs structure in Mg alloys wouldbe promising in future development of high-strength Mg-RE alloys. Japanese scholars placed great emphasison the importance of LPSO structure.(4) Other properties should be considered at the same timeof high strength. For example, the strong basal texturevia deformation processes is to the disadvantage of mechanical isotropy and secondary formability.(5) In view of the value of RE resources, the development of RE-containing Mg alloys should consider howto achieve high strength on the basis of low RE content(that is also low cost) without waste of RE resources.(6) Besides the alloying design, the process control is veryimportant for high-strength of Mg-RE alloys, especiallyin low RE containing Mg alloys.