Effect of microstructure and heat treatment of hypereutectic Al-Si alloys obtained by Rapid Solidification

Huircapan, Marcela Pichipil; Franco, Mercedes; De Rosa, Horacio

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Artículos • Matéria (Rio J.) 27 (02) • 2022 • https://doi.org/10.1590/1517-7076-RMAT-2021-49007 copy

Effect of microstructure and heat treatment of hypereutectic Al-Si alloys obtained by Rapid Solidification

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Eutectic AA-4032 alloy is widely used in internal combustion engine pistons due to its good combination of properties at intermediate temperatures. An important improvement in the properties could be obtained by increasing the Si fraction in Rapidly Solidified (SR) alloys and subsequently compacted, thus avoiding the formation of large Si plates characteristic of hypereutectic alloys. However, although there are several studies on its mechanical behavior, the study of its behavior against corrosion is still incomplete.

In this work, two hypereutectic alloys were studied, with 20%wt and 30%wt of Si, obtained by RS and compaction by Hot Extrusion, in comparison with the eutectic AA-4032 alloy (12%m of Si). Subsequently, Solubilization heat treatments (1h-530ºC) and artificial aging (170ºC-10hs) were carried out.

Microstructural characterization was carried out using X-ray Diffraction and Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX). The behavior against corrosion was analyzed by potentiodynamic polarization tests in 0.1M and 1M NaCl solution at room temperature and neutral pH. The surfaces of the tested specimens were morphologically characterized by SEM and EDX. The influence of the Si content in the alloys and its distribution in the microstructure on the shape of the polarization curves and their characteristic parameters is discussed.

Microstructurally, it was observed that the SR process prevented the formation of the primary Si plates, while the heat treatments promoted, among other things, the spheroidization of intermetallic particles. On the other hand, the corrosion tests showed that: the pitting potential of the alloys turns out to be independent of the Si content, the solubilized samples presented the lowest passivation current and all cases the preferential dissolution of aluminum occurs.

Keywords
AA-4032; Microstructure; Corrosion; Rapid Solidification

CÓDIGO	COMPOSICIÓN NOMINAL	CARACTERÍSTICA GENERALES
AA-4032	Al-12Si-1Cu-1Ni-1Mg-0.5Fe	Aleación eutectica – Solidificación Convencional
SR-446	Al-20Si-3.5Cu-2Ni-1.1Mg-2Fe	Aleación hipereutectica – Sol. Rápidamente + Consolidación en caliente
SR-444	Al-30Si-1.5Cu-1.5Ni-1.1Mg-1Fe	Aleación hipereutectica – Sol. Rápidamente + Consolidación en caliente

CÓDIGO DE TRATAMIENTO	PARÁMETROS Y DIAGRAMAS TECNOLÓGICOS DE LOS TRATAMIENTOS TÉRMICOS	IDENTIFICACIÓN DE LAS MUESTRAS TT
SB (Solubilizado)		4032 SB
		446 SB
		444 SB
T6 (Envejecimiento)		4032 T6
		446 T6
		444 T6

REF.	COMPOSICIÓN (% m)
REF.	Al	Si	Cu	Ni	Mg	Fe
α-Al	98,3	1,7
E	74,2	20,0	1,6	1,1	2,1	1,0
I	52,9	8,0	8,6	23,2	4,3	3,0

REF.	COMPOSICIÓN (% m)
REF.	Al	Si	Cu	Ni	Mg	Fe
E	70,8	27,1	1,4	–	0,7	–
B	67,6	18,0	–	–	10,3	4,1
I	61,6	7,9	6,7	15,2	1,2	7,4
Si	6,5	91,8	–	0,7	1,1	–

CÓDIGO DE MUESTRAS	POT_CORR (mV_ENH)	Z_PAS (mV)	I_PAS E⁻⁰⁶ (A/cm²)	POT_PIC (mV_ENH)
AA-4032	-726 ± 2	333 ± 15	11 ± 4	-393 ± 1
SR-446	-599 ± 3	197 ± 8	7,1 ± 0,3	-402 ± 12
SR-444	-616 ± 7	224 ± 7	13 ± 5	-392 ± 6
SB-4032	-735 ± 2	417 ± 15	1,5 ± 0,3	-318 ± 15
SB-446	-707 ± 12	384 ± 5	1,06 ± 0,2	-323 ± 4
SB-444	-714 ± 3	340 ± 16	1,03 ± 0,04	-374 ± 8
T6-4032	-718 ± 20	329 ± 8	1,9 ± 0.2	-389 ± 6
T6-446	-686 ± 4	351 ± 4	2,4 ± 0.7	-335 ± 5
T6-444	-687 ± 12	336 ± 6	2,5 ± 0.7	-351 ± 13

MUESTRA	REF	Al	Si	O	Cu	Ni	Fe	Mg	Cl
MUESTRA	REF	COMPOSICIÓN (%m)
AA-4032	M	65,62	11,78	18,53	1,39	0,61	0,64	1,43	–
AA-4032	PC	35,4	1,80	62,35	–	–	–	0,45	0.45
SR-444	M	37.4	37.4	19.2	2.25	1.57	0.9	1,28	–
SR-444	PC	33.5	–	65	–	–	–	–	1.5
SR-446	M	55.6	16.4	20.8	2.2	1.10	2.2	1.7	–
SR-446	PC	38.85	–	60.15	–	–	–	–	1

MUETRAS	ZONA	REF.	Al	Si	Cu	Ni	Fe	Mg
4032-SB	Dendritas	α-Al	96	2.5	1.1	–	–	0.4
	Eutectico	E	74	22	1	0.8	0.6	1
	Part. Blancas	PB	70.5	14	2	9	*2.5*	2
4032-T6	Dendritas	α-Al	*95.5*	2.8	1.3	–	–	0.2
	Eutectico	E	69	25.5	1.5	1	1	1.5
	Part. Blancas	PB	70	8.5	6.75	*8.5*	*2.25*	*4.5*

MUESTRA	ZONA	REF	Al	Si	Cu	Ni	Fe	Mg
444-SB	Aleación		55	42.1	1.5	0.25	0.7	0.45
	Part. Blancas	PB	59	7	7.5	17	8	1.5
	Part. Grises*	PG	20	77	1	1	0.5	0.5
444-T6	Aleación		55.05	41	1.6	0.8	0.95	0.6
	Part. Blancas	PB	55	17	6.5	12	7	1.9
	Part. Grises	PG	32	62.5	1	0.5	2.0	3.0

MUESTRA	ZONA	REF.	Al	Si	Cu	Ni	Fe	Mg
446-SB	Aleación		66.45	29.3	1.5	0.9	1	0.85
	Part. Blancas	PB	57.0	6.0	8	19.5	8	1.5
	Part. Grises*	PG	26.3	71.8	0.17	0.35	0.6	0.75
446-T6	Aleación		67.15	28.9	1.3	1	1	0.65
	Part. Blancas	PB	62	16	6	10	6	0
	Part. Grises	PG	42.5	53	1	1	1.5	1.0

MUESTRAS (%m)	Pot_CORR (mV_enH)	REF.
Al puro	-1035	RALSTON [³⁹[39] RALSTON, K., FABIJANIC, D., BIRBILI, N., “Effect of grain size on corrosion of high purity aluminium”, Electrochimica Acta, v. 56, n. 4, pp. 1729–1736, 2011.]
AA-4032 (12%Si)	-726	Presentado enEste trabajo
Al-4.93Si-3.47Cu	-960	Wiengmoon et. al [⁴⁰[40] Wiengmoon, A., Sukchot, P., TAREELAP, N., et al., “Effect of T6 heat treatment with double solution treatment on microstructure, hardness and corrosion resistance of cast Al-Si-Cu alloys”, Archives of Metallurgy and Materials, v. 60, n. 2, pp. 881–886, 2015.]
Al-6Si-0.5Mg	-504	Hossain et. al [⁴¹[41] Hossain, A., Gulshan, F., Kurny, A., “Electrochemical investigation of corrosion behavior heat treated Al-6Si-0.5Mg-xCu (x=0, 0.5, 1, 2 and 4wt%)”, International Journal of Corrosion, v. 2014, 356752, 2014.]
Al-6Si-0.5Mg-4Cu	-343	Hossain et. al [⁴¹[41] Hossain, A., Gulshan, F., Kurny, A., “Electrochemical investigation of corrosion behavior heat treated Al-6Si-0.5Mg-xCu (x=0, 0.5, 1, 2 and 4wt%)”, International Journal of Corrosion, v. 2014, 356752, 2014.]
Al-7Si-0.7Mg	-440	Revilla et. al [⁴²[42] Revilla, I., De Graeve, I., “Influence of Si content on the microstructure and corrosion behavior of additive manufactured Al-Si alloys”, J. of The Electrochemical Society, v. 165, n. 13, pp. C926–C932, 2018.]
Al-7.34Si-0.45Fe	-593	KUCHARIKOVa et. al [³⁷[37] Kucharikova, L., Liptakova, T. TILLOVÁ, E., et al., “Role of chemical composition in corrosion of aluminum alloys”, Metals, v. 8, n. 8, 581, 2018.]
Al-7.32Si-0.65Fe	-610	KUCHARIKOVa et. al [³⁷[37] Kucharikova, L., Liptakova, T. TILLOVÁ, E., et al., “Role of chemical composition in corrosion of aluminum alloys”, Metals, v. 8, n. 8, 581, 2018.]
Al-12Si	-360	Revilla et. al [⁴²[42] Revilla, I., De Graeve, I., “Influence of Si content on the microstructure and corrosion behavior of additive manufactured Al-Si alloys”, J. of The Electrochemical Society, v. 165, n. 13, pp. C926–C932, 2018.]

Fase	Intermetálico	Pot_CORR (mV_enH)
Fase	Intermetálico	0,01M	0,1M	0,6M
Al	–	–1040	–1200	–1350
B	Al₃Fe	–252	–298	–325
ϴ	Al₂Cu	–351	–424	–454
β	Al₃Zr	–511	–535	–560
–	Al₆Mn	–598	–538	–672
β	Al₃Ti	–379	–362	–558
T’	Al₃₂Zn₄₉	–768	–763	–822
β	Mg₂Al₃	–883	–772	–921
M, η	MgZn₂	–760	–788	–854
β	Mg₂Si	–1114	–1297	–1295
–	Al₇Cu₂Fe	–308	–310	–323
–	Mg(AlCu)	–657	–702	–695

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E-mail: revmateria@gmail.com

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[1] e-mail: mpichipil@fi.uba.ar, mmfranco@fi.uba.ar, hdrosa@fi.uba.ar