Experimental study of scandium addition and precipitate formation on the mechanical and tribological properties of Ultrasonic-assisted stir-cast AA7075 hybrid metal matrix composites

Ponnusamy, Mathiyalagan; Rajendran, Ashok Raj; Dhanaraj, Antony Prabu; Karuppiah, Panneer Selvam

doi:10.1590/1517-7076-RMAT-2024-0694

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Articles • Matéria (Rio J.) 30 • 2025 • https://doi.org/10.1590/1517-7076-RMAT-2024-0694 linkcopy

Experimental study of scandium addition and precipitate formation on the mechanical and tribological properties of Ultrasonic-assisted stir-cast AA7075 hybrid metal matrix composites

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Aluminium Alloy Hybrid Metal Matrix Composites (AAHMMCs) have been utilized in automotive, marine, military and aerospace applications due to their high strength-to-weight ratio, microhardness, tensile, impact, and compressive strength, along with superior tribological properties. This study focused on optimizing ultrasonic-assisted stir casting of AA7075/WC/SiC Hybrid Metal Matrix Composites (HMMCs) by varying the wt.% of WC and SiC (6, 8, and 10), melting temperature (700, 750, and 800°C), stirring time (5, 10, and 15 min), and stirring speed (200, 225, and 250 rpm), while keeping ultrasonic parameters constant. The inclusion of 0.25 and 0.5 wt.% Scandium increased microhardness by 18% due to the Hall-Petch effect and Al₃Sc precipitates, which strengthened the material. Ultrasonic assistance improved grain refinement and uniform particle distribution. The optimal process parameters were determined as a 750°C melting temperature, 250 rpm stirring speed, 5 min stirring time, and 8 wt.% WC+SiC. Aging at 300°C improved microhardness (by 15%), tensile strength (by 14.3%), compressive strength (by 12.4%), and wear resistance (by 51%) due to Mg₂Si and Mg₂Zn precipitates. Aging at 400°C increased impact strength by 59%, attributed to Al₂Cu precipitate.

Keywords:
Aluminium Alloy; Stir casting; Ageing temperature; Mechanical properties; Tribological properties

ELEMENTS OF AL7075
Elements		Si	Fe	Cu		Mg	Mn		Zn	Cr		Ti	Al
Wt.%		0.39	0.49	1.8		2.8	0.28		5.7	0.25		0.18	Rem.
ELEMENTS OF WC AND SIC
Elements	WC							SiC
Elements	W				C			Si			C
Wt.%	75.63				24.06			66.4			33.6

S.NO	DESCRIPTION	PROPERTIES
S.NO	DESCRIPTION	AA7075	WC	SIC
1	Particle size	–	20 µm	50 µm
2	Purity	98.5%	99%	99.5%
3	Density	2.81 g/cm³	15.63 g/cm³	3.21 g/cm³
3	Melting point	635ºC	2730ºC	2870ºC
4	Thermal conductivity	130 W/(m-K)	110 W/(m-K)	490 W/(m-K)
5	Tensile strength	240 MPa	344 MPa	390 MPa
6	Hardness	94 HV	800 HV	2563 HV
7	Compressive strength	340 MPa	1404 MPa	2000 MPa
8	Youngs modulus	71.7 GPa	530 GPa	90 GPa

EX. NO	MELTING TEMPERATURE ºC	BLENDING SPEED REV/MIN	STIRRING DURATION MINUTES	WT.% OF WC AND SIC	WT.% OF SC
1	700	200	5	6	0.25 & 0.5
2	700	225	10	8
3	700	250	15	10
4	750	200	10	10
5	750	225	15	6
6	750	250	5	8
7	800	200	15	8
8	800	225	5	10
9	800	250	10	6

EX. NO	STIRRING SPEED RPM	MELTING TEMPERATURE ºC	STIRRING DURATION MINUTES	WT.% OF WC AND SIC	WT.% OF SC
EX. NO	STIRRING SPEED RPM	MELTING TEMPERATURE ºC	STIRRING DURATION MINUTES	WT.% OF WC AND SIC	0.25	0.5
1	200	700	5	6	98	118
2	225	700	10	8	106	124
3	250	700	15	10	108	120
4	200	750	10	10	102	120
5	225	750	15	6	105	122
6	250	750	5	8	119	138
7	200	800	15	8	107	118
8	225	800	5	10	112	120
9	250	800	10	6	105	123

LEVEL	MELTING TEMPERATURE (ºC)	STIRRING SPEED (RPM)	STIRRING DURATION (MINUTES)	WT.% OF WC AND SiC
1	120.7	118.7	123.7	121.0
2	125.0	122.0	122.3	125.0
3	120.3	125.3	120.0	120.0
Delta	4.7	6.7	3.7	5.0
Rank	3	1	4	2

S.NO	2 HRS AGING DURATION	VICKERS MICRO HARDNESS
S.NO	2 HRS AGING DURATION	TRIAL 1	TRIAL 2	TRIAL 3	AVG
1	Non aged	138	139	137	138
2	Aged at 250°C temperature	149.2	148.8	149.4	149.2
3	Aged at 300°C temperature	160	159	158	159
4	Aged at 350°C temperature	146	145.6	145.2	145.6
5	Aged at 400°C temperature	152.4	152	152.8	152.4

S.NO	2 HRS AGING DURATION	TENSILE STRENGTH (MPa)
S.NO	2 HRS AGING DURATION	TRIAL 1	TRIAL 2	TRIAL 3	AVG
1	Non aged	286	286.5	287	286.5
2	Aged at 250°C temperature	299.2	298	298.6	298.6
3	Aged at 300°C temperature	326.4	327.2	328.4	327.3
4	Aged at 350°C temperature	315.2	315	316.2	315.5
5	Aged at 400°C temperature	320.1	320	320.6	320.2

S.NO	2 HRS AGING DURATION	COMPRESSIVE STRENGTH (MPA)
S.NO	2 HRS AGING DURATION	TRIAL 1	TRIAL 2	TRIAL 3	AVG
1	Non aged	378	377	378	377.7
2	Aged at 250°C temperature	396	398	397	397.0
3	Aged at 300°C temperature	423	424	423	423.3
4	Aged at 350°C temperature	411	412	411	411.3
5	Aged at 400°C temperature	416	418	417	417.0

S.NO	2 HRS AGING DURATION	IMPACT STRENGTH (J)
S.NO	2 HRS AGING DURATION	TRIAL 1	TRIAL 2	TRIAL 3	AVG
1	Non aged	2.47	2.49	2.47	2.48
2	Aged at 250°C temperature	2.88	2.86	2.88	2.87
3	Aged at 300°C temperature	3.62	3.66	3.64	3.64
4	Aged at 350°C temperature	3.42	3.44	3.46	3.44
5	Aged at 400°C temperature	3.96	3.98	3.94	3.96

APPLIED LOAD (N)	WEAR LOSS (mg)
APPLIED LOAD (N)	NON AGED	250°C	300°C	350°C	450°C
10	33	25	16	28	18
20	39	31	24	34	27
30	46	38	30	42	32
40	52	47	39	50	43

APPLIED LOAD (N)	CoF (µ)
APPLIED LOAD (N)	NON AGED	250°C	300°C	350°C	450°C
10	0.36	0.41	0.45	0.39	0.42
20	0.39	0.46	0.51	0.43	0.46
30	0.44	0.51	0.56	0.47	0.51
40	0.49	0.57	0.62	0.54	0.59

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Laboratório de Hidrogênio, Coppe - Universidade Federal do Rio de Janeiro, em cooperação com a Associação Brasileira do Hidrogênio, ABH2 Av. Moniz Aragão, 207, 21941-594, Rio de Janeiro, RJ, Brasil, Tel: +55 (21) 3938-8791 - Rio de Janeiro - RJ - Brazil
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