Fig. 1 and Fig. 2 show the SEM photos of as cast samples of A1 and A2 alloys without ultrasonic treatment. It can be seen that the microstructure of as cast alloys mainly includes Al matrix, primary Si, coarse needle like primary iron rich phase and eutectic Si, al2cu and as cast samples without ultrasonic treatment and extrusion pressure The eutectic structure is composed of alcuni. It can be seen from Fig. 3 that when no extrusion force is applied, the main iron rich phase in A1 alloy is long white acicular β phase with an average length of 120 ± 41 μ M. the length of clockwise β phase decreases obviously with the extrusion force increasing. Under the extrusion pressure of 100, 200 and 300 MPa, the as cast microstructure of A1 alloy is decreased The length of middle β phase was 86 ± 28, 67 ± 23 and 62 ± 19 μ m, respectively.

It can be seen from Fig. 2 that, in addition to long needle like β phase, there are also lath like δ phase in the microstructure of A2 alloy without extrusion force. The EDX analysis results show that the iron rich phase in A2 alloy is composed of long needle like β phase and lath like δ phase. The results show that the length of β phase in A2 alloy is 0, 100, 200 and 300 MPa respectively The length of δ phase is 169 ± 60,154 ± 48,125 ± 37,107 ± 33 μ m, which means that the length of iron rich phase decreases with the increase of extrusion pressure.

Compared with Fig. 1 and Fig. 2, the length of β phase in A2 alloy is longer than that in A1 alloy under the same extrusion pressure, which is due to the higher Fe content in A2 alloy.