Introduction
Experimental Details
Material Preparation
Zn | Mg | Cu | Fe | Si | Mn | Cr | Ti | Al |
---|---|---|---|---|---|---|---|---|
5.96 | 2.57 | 1.88 | 0.3 | 0.11 | 0.15 | 0.23 | 0.03 | Balance |
Process | Operation | Plating bath composition | (/L)
| Condition |
---|---|---|---|---|
1 | Grinding | No. 1000 SiC sandpaper | ||
2 | Degreasing bath | Na2CO3
| 10 g | 65 °C for 2 min |
Na3PO4·12H2O | 50 g | |||
3 | Etching bath | Conc. H2SO4
| 40 mL | 65 °C for 2 min |
H3PO4
| 20 mL | |||
DM water | 40 mL | |||
Propionic acid, C3H6O2
| 0.1 mL | |||
Distilled with deionized water | Room temperature | |||
4a | Pretreatment bath for Zn (zincate) | NaOH | 400 g | Room temperature for 1 min |
ZnSO4·7H2O | 120 g | |||
Sodium potassium tartarate | 06 g | |||
4b | Pretreatment bath for Ni strike | NiSO4·7H2O | 28 g | Room temperature for 1 min |
HF, 40% | 90 g | |||
H3BO3
| 40 g | |||
4c | Pretreatment bath for absorbed HP adlayer | NaH2PO2·H2O | 30 g | 80 °C at pH 4.5 for 5 min |
Lactic acid, 80%,C3H6O3
| 20 mL | |||
5 | Electroless Ni-P | NiSO4·6H2O | 0.1 mol | 85 °C at pH 6 for 120 min |
NaH2 PO·H2O | 0.35 mol | |||
C2H5 NO2
| 0.09 mol | |||
C3H6O3
| 0.40 mol | |||
C3H6O2
| 0.02 mol | |||
CuSO4
−
| 04 ppm | |||
CH3·COO(Pb−)·3H2O | 01 ppm | |||
Distilled with deionized water | Room temperature |
Pretreatments
-
Ni strike. The nickel immersion plating solution contained hydrogen fluoride, nickel salts and boric acid. The process was kept for 1 min at room temperature. A thin film of Ni was produced on aluminium alloy by contact reduction type reaction between substrate and nickel salt solution. The Ni nucleus on the aluminium substrate effectively produced and acts as a catalyst for the succeeding electroless Ni-P plating.
-
Zinc immersion (zincate). The zinc immersion plating solution contained sodium hydroxide, zinc sulphate and sodium potassium tartarate. The process was kept for 1 min at room temperature. A thin film of Zn was produced on aluminium alloy and it protects the aluminum against re-oxidation. The zinc precoating tends to sacrifice itself during the Ni-P depositing due to the sacrificial corrosion of zinc.
-
Hypophosphite absorbed layer. The hypophosphite absorbed pretreatment solution contained sodium hypophosphite and lactic acid at pH 4.5. The process was kept for 5 min at 80 °C temperature. A thin film of HP was produced on aluminum alloy and it acts as a catalyst for the succeeding electroless Ni-P plating.
Dry Sliding Wear
Friction and Hardness
Surface Morphology Studies
Results and Discussion
Sliding Wear and Hardness
Different pretreatment | Average co-efficient of friction (μav) (a) | |
---|---|---|
Ni-P (h) heat treated at 200 °C/1 h | Ni-P (h) heat treated at 400 °C/1 h | |
Absorbed HP adlayer | 0.610 | 0.582 |
Zn (zincate) | 0.523 | 0.376 |
Ni strike | 0.445 | 0.240 |
Morphology and Components of EN Wear Track
Conclusions
-
All the pretreated coatings improve the wear behavior of the 7075 aluminum alloy substrate. The wear behavior of EN mostly depends on the pretreatment conditions. Heat-treatment temperature of 400 °C showed superior wear resistance properties of all types of pretreatment condition samples.
-
The remark that is emphasized in all the cases is that the EN/Ni deposit on 7075 Al substrate shows noticeably enhanced wear resistance, high hardness and improved frictional behavior among the three different pretreatments and these properties were further enhanced by heat treatment at 400 °C/h. Furthermore, the beneficial effect of three pretreatments was estimated according to their wear performance as: Ni strike > Zn immersion > HP absorbed layer.