Transcript Vickers Microindentation Hardness Testing of Brazed Joints

Vickers Microindentation Hardness
Testing of Brazed Joints in Aluminum
Patricia B. Roy, Fiona M. O’Connell,
Thomas H. Callahan, Edward J. Armellino,
and Wayne L. Elban
Department of Engineering
Loyola University Maryland
Baltimore, Maryland 21210
27th Annual National Educators' Workshop NEW: Update 2012
November 4 – 7, 2012, Fort Wayne, Indiana
Joining Metals by Brazing
• Brazing is the joining of two base metals via a
filler metal.
• Brazing operations apply heat broadly to the
base metals.
• The filler metal is then placed into contact
with the base metals and melts.
• The filler metal wicks into the joint via
capillary action.
extrusion
3003 Al core
Polished Cross-section of Vacuum-brazed
Aluminum Alloy Sample
extrusion
fins
4004 Al liner
part of
extrusion 5
part of extrusion 1
extrusion 2
extrusion 3
extrusion 4
3.5 mm
area where
microhardness
indentations are
Learning Goals
• To become familiar with:
– Vickers microindentation hardness testing, a
prominent technique for characterizing the
mechanical response of materials
– brazing technology
– the process of creating a computer-based
mechanical property correlation for various
materials
Experimental Goals
• To measure the Vickers hardness profile across
a set of brazed joints in an aluminum alloy;
and
• To obtain a computer-based mechanical
property correlation
Vickers Hardness Testing
Taken from “Tukon Microhardness Testers,” Page-Wilson Crop.
(Instron). Bulletin 1830 (1982)
• Square-base diamond
pyramid indenter
• 10 gf to 1,000 gf applied
load for a range of 0-30
seconds dwell
• Resulting indentation
formed by plastic
deformation
• Diagonal length
measured optically
Vickers Hardness Number (VHN)
VHN calculated using
VHN = 1.8544 P/d2
where
P= Applied load, kgf
d= Indentation diagonal length, mm
VHN [=] kgf/mm2
Experimental
• Calibrate using standard reference test block
• Perform series of twenty hardness
determinations using 10 gf applied load for 25
seconds dwell
– Over 5.875 mm distance perpendicular to four
brazed joints to obtain hardness profile
Data Analysis
• Compute VHN for each hardness impression
• Plot tensile strength versus Knoop hardness
number (KHN) using Wilson (Instron) Desk
Chart 60
• Obtain tensile strength estimates for VHN
determinations
Photomicrograph of Left-hand Brazed
Joint Assembly
8
5
2
3
7
Hardness Profile of Two Brazed Joint
Assemblies
Vickers Microindentation Hardness vs. Distance
120.0
3
VHN, kgf/mm^2
100.0
7
11
1
80.0
16
12
9
18
60.0
14
40.0
5
20.0
0.0
0
1
2
3
Distance from Sample Edge, mm
4
5
6
Tensile Strength - Knoop Hardness Number
Correlation (from Wilson Desk Chart 60; 500 gf)
Tensile Strength vs. Knoop Hardness
Tensile Strength, ksi
140
120
y = 0.4641x - 3.5055
R² = 0.9924
100
80
60
40
20
0
120
140
160
180
200
KHN
220
240
260
Hardness Values with Corresponding
Tensile Strength Estimates
VHN, kgf/mm2
70.7
74.3
95.3
Tensile Strength Est., ksi
29.3
31.0
40.7
1st extrusion
1st extrusion, near braze
braze
4
5
62.0
38.5
25.3
14.4
m. 3003 core sheet, very near braze
modified 3003 core sheet, center
6
7
8
9
19
20
10
11
12
58.9
92.0
63.0
68.5
65.7
68.1
77.7
85.8
88.2
23.8
39.2
25.8
28.3
27.0
28.1
32.5
36.3
37.4
m. 3003 core sheet, very near braze
braze
nd
2 extrusion, very near braze
2nd extrusion, center
2nd extrusion, center
2nd extrusion, center
2nd extrusion, very near braze
braze
braze
13
14
69.4
55.4
28.7
22.2
m. 3003 core sheet, very near braze
modified 3003 core sheet, center
15
16
17
18
58.5
89.4
60.9
68.1
23.7
38.0
24.8
28.1
m. 3003 core sheet, very near braze
braze
rd
3 extrusion, very near braze
3rd extrusion, toward center
Imp. #
1
2
3
Location
Hardness Insights
• Highest hardness values found at impressions
#3, 7, 12, and 16 in the actual brazed joints
• Elevated hardness found in regions closest to
brazed joints at impressions #4, 6, 13, and 15
• Lowest hardness found at nominal centers of
3003 core sheets at impressions #5 and 14
• High hardness values due to solid solution
hardening and precipitation hardening of filler
metal
Tensile Strength Comparison
Material
Tensile Strength
Source
Modified
3003-H24 Al
(estimates)
14.4 and 22.2 ksi
Current Work
3003-O
16.0 ksi
Literature
3003-H22 Al
23.0 ksi
Computer-based Mechanical Property
Correlation
• Cambridge Engineering Selector (CES) EduPack
2012 software
• Plot generated: tensile strength versus Vickers hardness
• Labeled materials:
–
–
–
–
–
–
–
–
–
Alumina
Aluminum alloys
Bamboo
Cellulose polymers (CA)
CFRP, epoxy matrix (isotropic)*
Flexible polymer foam (MD)
Silica glass*
Stainless steel
Stone*
* Has estimated material property
Tensile Strength vs. Vickers Hardness
Mechanical Property Correlation
Insights
• Expected strong correlation: tensile strength
increases with increasing hardness
– Tensile strength = highest measured load divided
by initial area and typically associated with plastic
deformation
– Vickers hardness gives measure of a material’s ease
to deform plastically in accommodating the
indenter
Acknowledgements
Dr. S.F. Baumann
ALCOA Mill Products
Heat Exchanger Products Technical Center
1480 Manheim Pike
Lancaster, Pennsylvania 17601
Dr. M.R. Staker
Department of Engineering
Loyola University Maryland
Baltimore, MD 21210
Extra Slides to Follow
(for possible discussion issues)
Photomicrograph of Right-Hand Side
Brazed Joint Assembly
10
12
14
16
Indenter Load Effect
Vickers Hardness vs. Applied Indenter Load for
Modified 3003 Core Sheet Al (Center)
VHN, kgf/mm^2
70
LH Joint Assembly
60
RH Joint Assembly
50
40
30
20
0
0.1
0.2
Load, kgf
0.3
0.4
0.5
0.6