The microstructure and mechanical properties of the Al-5.0Mg-0.6Mn-0.25Ce alloys prepared by sand casting

metal casting and die-casting were investigated by OM

SEM

EDS and tensile testing.The results show that with the increase of cooling rate

theα-Al dendrites in the casting alloy are transformed into roundα-Al grains

and the second phase is refined.With a lower cooling rate

the as-cast microstructure of sand casting and metal casting alloy mainly consists ofα-Al dendrite

Al

3

Mg

2

phase

Al

6

（Fe

Mn）phase

Mg

2

Si phase.While with a higher cooling rate

the die-casting alloy consists of small equiaxedα-Al grains and short rod-shaped Mn-containing phases as well as needle-shaped Mg

2

Si phases distributed around the grain boundaries.With the increase of the cooling rate

the yield strength and tensile strength of the casting alloys are gradually increased

while the elongation rate is increased firstly and then decreased

which is mainly attributed to the microstructure of the alloy and the casting defects such as shrinkage holes.When the cooling rate increases

the microstructure of the casting alloys become finer

and the more Mg and Mn are dissolved into theα-Al-based matrix

leading to the higher strength of the alloys.However

in die-cast alloy

there exists gas hole and needle Mg

2

Si phases

which is harmful to the plasticity of the alloy.