Effect of heat treatment on mechanical property and corrosion behaviour of selective laser melted Al-Mn-Mg-Sc-Zr alloys
The selective laser melted(SLM)alloy was prepared at laser power of 330 W and scanning speed of 700 mm/s using Al-4.77Mn-1.37Mg-0.67Sc-0.25Zr(mass fraction,%)alloy powder as raw material.The effects of heat treatment(350℃,8 h)on mechanical properties and corrosion behavior of SLM Al-Mn-Mg-Sc-Zr alloy were analyzed by slow strain rate tensile test,electrochemical test,hydrogen evolution test and microstructure characterization.The results show that the mechanical properties of SLM Al-Mn-Mg-Sc-Zr alloy are excellent,the tensile strength,yield strength and elongation reach 423 MPa,376 MPa and 25.1%,respectively.After heat treatment,a large number of needle-like or rod-like Al6Mn phases precipitate,and the tensile strength and yield strength further increase to 509 MPa and 478 MPa,respectively.In addition,SLM Al-Mn-Mg-Sc-Zr alloy has good corrosion resistance,heat treatment can promote the passivation of SLM Al-Mn-Mg-Sc-Zr alloy at polarization potential of-0.5 V,decrease the current density of SLM Al-Mn-Mg-Sc-Zr alloy and increase anode polarizability of SLM Al-Mn-Mg-Sc-Zr alloy.Therefore,the average hydrogen evolution rate of SLM Al-Mn-Mg-Sc-Zr alloy decreases from 0.242 mL/(cm2·h)to 0.216 mL/(cm2·h),and the stress corrosion sensitivity factor of SLM Al-Mn-Mg-Sc-Zr alloy decreases from 3.379%to 0.405%.At the same time,the heat treatment can also accelerate the precipitation of micron-scaled Si-rich phase of SLM Al-Mn-Mg-Sc-Zr alloy in grains and Mn and Mg enriched grain boundary phases,which increases the nucleation sites of pitting corrosion nucleation and the non-uniformity of the electrochemistry at the grain boundary,reduces resistance to pitting corrosion and intergranular corrosion.
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