Shortened processing duration of high-performance Sm-Co-Fe-Cu-Zr magnets by stress-aging

Simultaneously achieving high energy product and high coercivity in the 2:17-type Sm-Co-Fe-Cu-Zr high temperature magnets has been closely relied on long-term isothermal aging to develop complete cellu-lar nanostructure.In this work,we report a novel stress-aging approach that can substantially shorten the aging time to fabricate high-performance Sm-Co-Fe-Cu-Zr magnets.As exhibited by a model magnet Sm_(25) Co_(50.2) Fe_(16.2) Cu_(5.6) Zr_(3.0)(wt.%),applying 90 MPa compressive stress can shorten the aging time from 20 h for conventional isothermal aging to 10 h at the same aging temperature for achieving nearly equiv-alent magnetic performance.Further comparative study between the 10 h-aged samples under stress-containing and stress-free conditions revealed that the stress not only promotes the precipitation of the cell boundary phase that are essential for enhancing the coercivity but also accelerates the dissociation of the cell edge defects that are detrimental to squareness factor,without destroying the[001]crystal-lographic texture.Such microstructural improvements enable the achievement of high-performance with maximum energy product of∼30 MGOe and coercivity above 35 kOe at reduced aging time.

Synchronous improvement of mechanical properties and stress corrosion resistance by stress-aging coupled with natural aging pre-treatment in an Al-Zn-Mg alloy with high recrystallization fraction

Enhancing the strength of Al-Zn-Mg alloys is critical to the weight-lightening of structural components in the application of high-speed trains and aerospace industries,while high stress corrosion cracking(SCC)susceptibility of Al-Zn-Mg alloys(especially the alloy with high recrystallization fraction)with high strength makes it difficult.In this study,the influence of tensile stress-aging coupled with natural aging pre-treatment on the mechanical properties and SCC resistance of Al-Zn-Mg alloy with high recrystallization fraction has been investigated.The results show that tensile stress-aging at 160℃can inhibit the dissolution of clusters/Guinier-Preston(GP)zones formed during long-term natural aging pre-treatment,which increases the number density of matrix precipitates(MPts),narrow the width of precipitate free zone(PFZ),and dramatically improve the mechanical properties of the experimental Al-Zn-Mg alloy.Meanwhile,the precipitation of the high density of MPts within the matrix will assume a large number of solute atoms during artificial aging,which will reduce the supplement of solute atoms to grain boundaries.As a result,the volume of anodic active grain boundary precipitates(GBPs)and the content of free solute atoms at grain boundaries are reduced,which reduces the possibility of initial nucleation and propagation of SCC crack.The coupled treatment method proposed in this study proves efficient in resolving the contradiction between the strength and SCC resistance in Al-Zn-Mg alloy.