The as-cast microstructure and homogenization treatment of semi-continuous casting AZ40 ingot with a diameter of 500 mm were investigated.Dendrites and compounds in the center of ingot are coarser than those in the outer.In as-cast microstructure

Al enrichment zones with Al content of about2.62% exist at the edges of dendrites

however

the Al content in the center of dendrites is only about0.59%

and other Al atoms are used to form Mg17Al12 and Al-Mn compounds.Zn and Mn atoms are uniformly dissolved into dendrites

and Mn atoms are used to generate Al-Mn particles

and Zn atoms tend to enrich at Mg17Al12 particles.During homogenization treatment

Mg17Al12 can easily be re-dissolved into matrix

however

it is difficult for Al enrichment zones to uniformly diffuse from edges to centers.With homogenization treatment at 410 ℃ for 4h

eutectoids in the matrix are re-dissolved basically

while Al-enrichment zones can not be re-dissolved effectively.After homogenization treatment at 410℃for 24 h

Al enrichment zones are totally re-dissolved in the matrix with uniformly distributed Al content

and the Al content in most parts of matrix is approximately 4.02%.