Computational high-throughput design of ductile magnesium alloys

Magnesium alloys have an outstanding position in the search for  the  next-generation  light-weight  materials.  However,  their  application  is  still  hampered  by  their  inherent  brittleness.  Based on an interdepartmental, computational high-throughput strategy,  scientists  at  the  MPIE have  found  a  solution,  which  makes the material both ductile and affordable.

Thinking  about  light-weight  structural  materials,  e.g.,  for  automotive applications, Al alloys are often considered  first. Although  magnesium is 1.7 times lighter than Al and has  a  comparable  price,  its  brittleness makes applications very rare. A few alloying strategies to improve the  situation  have  been  suggested  in  recent  years,  but  are  mostly  ex-pensive  due  to  the  involvement  of  rather expensive and environment-unfriendly rare-earth elements such as  yttrium.  therefore,  we  have  optimized  the  ductility  of  Mg  alloys, by  screening  several  thousand  alloying  concepts  and  identifying  the  most promising and economical solution [1].

The   materials   science   approach   required in the first place a reliable yet  easily  accessible  descriptor  for  optimum    mechanical    properties.    the experimental investigation performed  at  the  department  “Micro-structural Physics and Alloy Design“ identified the intrinsic stacking-fault energy as such a candidate. In con-trast  to  the  dislocations  processes  required  for  the  complete  description  of  the  underlying  plasticity  [2],  this  energy  can  be  directly  calculated  by  ab  initio  calculation  em-ployed  in  the  department  “Computational  Materials  Design”.  A  direct  screening of 18 transition metals as possible  individual  solutes  did  not  identify  better  candidates  than  the  previously identified rare-earth element yttrium [3]. Instead, it allowed us  to  identify,  which  physical  properties  distinguish  the  mechanical  impact of yttrium from other solutes. Based on these insights, the yttrium similarity   index   (YsI,   approach-ing  1  for  yttrium-similar  elements)  was  identified  as  a  new  figure  of merit,  which  subsequently  allowed  to  screen  2850  solute  pairs  within  Mg with reasonable numerical effort (Fig.  1).  Nevertheless,  the  evaluation of such widerange studies requires a reliable data management system.   Our   recently   developed   software   framework   pyiron   does   not only provide such a tool for automated  data  generation,  storage,  analysis  and  visualization,  but  at the same time an integrated developing  environment  for  new  materi-als concepts. As a result of this design strategy a Mg-Al-Ca system, namely, Mg-1Al-0.1Ca  (wt.%)  was  found  to  show  promising mechanical performance (YsI  >  0.95),  while  still  being  in-expensive  and  non-toxic.  Only  afterwards,  the  tensile  stress-strain behaviour of this alloy was compared with pure Mg and binary solid solution Mg-re and Mg-Y alloys (Fig. 2). the result was outstanding: a tensile elongation of about 20% (4x more ductile than  pure  Mg),  a  well-balanced  constant work hardening, and an ultimate tensile  strength  of  about  220  MPa  (40% higher than pure Mg) [1]. Such a performance makes Mg alloys highly attractive for future materials science as well as light-weight applications.

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Authors: T. Hickel, J. Neugebauer